How to access iCloud backup and upgrade subscription for a new iPhone 15?

In February I upgraded from an iPhone 12 to an iPhone 15. All was fine and I had it all backed up through iCloud.

We also have a family MacBook which is on my iCloud, and an old iPad my son uses that is set-up through FamilyShare. My husband also has an iPhone but uses a separate iCloud.

Last week my iPhone 15 stopped working. I have been to the Apple Store and they have fixed it; it is effectively a new phone as the whole “computer part” was replaced.

I am now trying to set the fixed iPhone 15 up. As I couldn’t transfer from another device I selected back-up from iCloud, and it said there was no back-up, so it is now a

blank phone. I have logged into iCloud through the web and can see all the things backed up from the broken iPhone 15, but can’t access it. An error is coming up to say iCloud is full, so I have tried to update it for a bigger version but the payment method keeps failing. I have tried a few different cards and they all fail when it connects to the bank.

I have tried to update iCloud through the MacBook but it won’t accept the updated passwords.

So I am now stuck and very frustrated as am going around in circles. Please tell me there is an easy fix,l before it gets thrown from the window!

Summary of the rant:

-can’t get back-up iPhone15 from iCloud;

-can’t upgrade iCloud subscription.

Thank you for reading and for any suggestions.

[Re-Titled by Moderator]