How can I regain access to my Apple Account that’s been blocked?

I registered an account on the Apple website for my relative. He is in retirement and cannot do this on his own. Registration was successful, I entered the login and password on the iPhone and entered this account. One day everything was fine. The next day, a message appeared in the iPhone settings, something like "some more services are asking for confirmation of your Apple Id, enter your password." I entered the password, and the message "Apple Id is not active" appeared. I submitted an application on the Apple website to restore access to my Apple Id. The next day, a letter came to my email from the support service that my account was blocked and I can’t use it anymore. No explanation, no reason! What the ****, Apple? Now I have an iPhone with my Apple Id in my hands, which is blocked and I can’t get out of it to register a new one! I can’t discard the password on the support site, since when entering my data, I get a message that this account is blocked and cannot be used more. The iPhone is not new, I was not bought in the store, I bought it for cash, I have no documents about its purchase. What should I do?

[Re-Titled by Moderator]