Have you contacted the team through Live Support? I think it can be the fist one you need to try. Even if you reported the case in this thread, the team may be not always active here.  ;
If you have no problem to withdraw your balance in the past, there should be a problem with the phone or the phone number. Are you sure that the phone number is still active? It is a bit confusing that the message said for registration. I guessed you have registered with the phone number in the past, right?

It means you already have a functional 2FA authorization activated but still it doesn't work from time to time, well it depends on the format you are using if you are using your mobile authenticator where codes get sent to your mobile phone number, note that such otp may get blocked if, your country have regulations against such services.


Best way is to have 2FA application or device where you can generate your codes instead waiting to be sent a code.

So you are about to set your 2FA, and the mobile number hasn't been accepted? These aren't serious issues, so there's no need to panic. I assume you are using an incorrect format for your mobile number. Because likely they are asking for the international format of your mobile number. If you don't have privacy issues, you may share your country. So other users would help you with the correct format.

However, since you posted here, I believe the BC game support team would solve it. Try to reach them through support, so they might help you as well. Don't worry; the problem can be solved.