Hey @Red-Beretta937 Welcome to the Forums!
Sorry to hear that you are experiencing an error when trying to add your phone number to your account. Please make sure that your phone number has not been linked with another account as this may result in you receive this message.
Should you still encounter this Issue, I would suggest creating a support case on our support website, as we are unable to proceed with account related issues here on the forums.
Once you have created a case, one of our colleagues can take a closer look into your account for you.
Should you have any further queries, please let us know!