I am blocked to access my iPad.

You have encountered a Scam.

See >>> Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

Don’t respond to, or engage with, the message. Certainly do not, under any circumstances, attempt to contact anyone using the contact details that may have been provided. Alerts of this nature are designed to scare the unwary into giving away sensitive information - or to fool you into doing something that you shouldn’t - usually to defraud you financially.

If you are unable to close the associated alert/window, perform a forced restart of your iPad:

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

Providing your iPad has been kept up-to-date with system software updates, you should not be overly concerned for your iPad being directly compromised by malware.

For older devices, no longer benefiting from regular security updates, or those that are not kept up to date when system software updates are available, the risk of an unpatched vulnerability being exploited increases. 

Threat Mitigation

The majority of threats to which you will be invariably exposed will surface via web pages or embedded links within email or other messaging platforms. Browser-based attacks can be largely and successfully mitigated by installing a good Content and Ad-blocking product. One of the very best and most respected within the Apple App Store - designed for iPad, iPhone and Mac - is 1Blocker for Safari.

https://apps.apple.com/gb/app/1blocker-for-safari/id1365531024

1Blocker is highly configurable - and crucially does not rely upon an external proxy-service of dubious provenance. Instead, all processing by 1Blocker takes place on your device - and contrary to expectations, Safari will run faster and more efficiently.

Unwanted content is not simply filtered after download (a technique used by basic/inferior products), but instead undesirable embedded content is blocked from download. The 1Blocker product has also recently introduced its new “Firewall” functions - that are explicitly designed to block “trackers”. Being implemented at the network-layer, this additional protection works across all Apps. Recent updates to 1Blocker has introduced additional network extensions, extending protection to other Apps.

A further technique to improve protection from exploits is to use a security focussed DNS Service in preference to automatic DNS setting. These specialist DNS providers "sink-hole" malicious or compromised and malicious resources before your device is able to connect. This measure can either be set on a per-device basis in Settings, or can be set-up on your home Router - and in so doing extends the benefit of this specific protection to other devices on your local network. I suggest using one of the following DNS services - for which IPv4 and IPv6 server addresses are listed:

Quad9 (recommended)

9.9.9.9

149.112.112.112

2620:fe::fe

2620:fe::9

OpenDNS

208.67.222.222

208.67.220.220

2620:119:35::35

2620:119:53::53

Cloudflare

1.1.1.1

1.0.0.1

2606:4700:4700::1111

2606:4700:4700::1001

Use of the above DNS services will help to shield you from “known bad” websites and URLs - and when used alongside 1Blocker, or other reputable Content Blocker, provides defence in depth.

There are advanced techniques to further “harden” iOS/iPadOS (such as using DoH, DoT and DNSSEC). Apple has recently introduced its new Private Relay to its iCloud+ subscribers - in part employing ODoH (a variant of DoH) as an element of this new functionality. If you have subscribed to iCloud+, and have a device capable of running iOS/iPadOS 15.x or later, this feature is included.

Timing is critical - as otherwise you won't trigger the restart.

Steps #1 and #2 must be performed very quickly - immediately followed by step #3. Until practiced, you may not trigger the restart first time.

Given the recurrence, there is one potential source of potential issue that you may need to check - this being for a vulnerability that is often exploited that gives the appearance of a malware infection. This involves your iPad/iPhone Calendar - the symptom being your Calendar appearing to have been populated with regular events that warn of malware infection.

Calendar Infection

Whilst not a malware infection in the traditional sense, if this exploit is observed on your device, it is highly probable that you were manipulated (via a simple click on a website link) into “subscribing” an additional (unwanted) Calendar to your device - and this unexpected Calendar is exposing unwanted calendar events and sending you unexpected “adverts” or other warnings. 

If you see this issue, you’ll need to check for what’s out of place...

iOS/iPadOS13 and earlier: Settings > Passwords and Accounts

iOS/iPadOS14 and later: Settings > Calendar > Accounts

Look for an “account” that shouldn’t be in the list of accounts - as this will likely include the Calendar that contains all the unwanted events. When/if you find the suspect account, tap - then select Delete Account. This should resolve this specific problem in its entirety.

I had to re-read the above. All you did was restart the iPad, which fixed nothing, and wasn't even necessary.

If Safari is taking over the screen again, drag your finger up from the bottom of the screen to get your open apps to display (application switcher). Drag Safari up and off the screen to close the app. Next, go to:

Settings > Safari > Clear History and Website Data

This will wipe the garbage from your browser cache. You can then close the Settings app.

When you launch Safari again, it will pretty much behave as if you've never gone anywhere on the Internet. You may need to enter some passwords again for sites you visit that require one for access.

Avoid going back to the site that caused that junk to appear in the first place or it will simply happen again.

1Blocker is a very good idea. It will prevent a lot of junk like this from appearing. For a free option, there's Ka-Block!, which is available on the App Store and works very well.

LotusPilot's second post may also be correct. You didn't say how you're seeing these scam messages. So it could be popups in Safari, or from Calendar spam.

You're very welcome.

By not going to the web site that displays it.

You need to stop visiting the websites that have those pop-ups.