How to stop receiving spam mails on my iPhone?

If you are referring to Gmail they have a spam filter, and you can also add a custom spam filter, maybe it requires a bit of reading but surely it'll improve your situation.

Rivers2libra39 wrote:

I continuously keep receiving emails I know I didn’t sign up for never ever visited those sites especially the dating sites, meeting singles sites, or sexual sites

Everyone who has an email account gets those.

But, as your account has been compromised by another person, KiltedTim's advice is the best.

IOT stop spam mail from being received is to either allow your e-mail provider to “smartly” discern it needs to be identified as such (if the feature be there) &/or create a filter for every piece of spam yi receive. The last 4+ iOS updates have claimed to include a stronger “smart” filter installed & unmodifiable within their e-mail app. I also recommend not allowing your spam folder to automatically empty aft a certain number of days, in the instance something important arrives & yi miss/lose an opportunity. I also recommend setting reminders every so oft to check your spam folder so that it doesn’t take up the allotted space & prevent further e-mails from being received.

There is nothing Apple or anyone else can do about it.

The best thing you can do at this point is to close that account and create a new email account.

The best you can do is to set a filter or activate a spam filter in your email account online, usually there's a way to block or activate a spam email filter