My own phone number is unavailable!!!THIS ACCOUNT IS EITHER NOT VALID OR NOT SUPPORTED.

So I was using an iPhone SE 2 and then it was stolen so my father gave me his unused one, but when I was trying to login through the number, it says the number is not available, I disabled the iMessage for that number and then I tried to login through that number but still the same thing happened so I tried to login through the email instead and it was successful. So I thought of resetting a password using that number and when I use that number to sign in on iforgot.apple.com it says that the account does not exist or there is something wrong with that account. To be clear, I used that number to sign in earlier and I want to use it but I cannot use it. I only got a single number. Apple did give me an amount of time to reset the password and in that given period of time it still says the same … Depressed