How to retrieve my old iCloud backup using my old phone number?

I need help getting back into my old iCloud back up with my old phone number, I want everything from my old phone back onto it, I dont want it updated and backed up to my new phone. I want access to my old phone number again. I haven’t been able to access my old phone number which still has many of my accounts attached, and without getting that phone number back I cannot access those accounts, and old contacts.

[Re-Titled by Moderator]