If you had passed the KYC before, they would have been able to help you change your old phone number after you submitted the legal documents, but how will they believe that you are the owner of the main account and you claimed that the number belonged to your girlfriend or that it was your old number, Perhaps they thought, like others, that it is not your account, and perhaps an account whose email and password you stole, excuse me, I do not say that you are a scammer, but I explain to you that it is difficult for the BigONE platform customer center to help you if they are not 100% sure that you are the main owner of the account, In any case, they mentioned to you that you need to submit a new video certificate with all the details they want and the declaration that you will make for yourself. After submitting this new video certificate, they can help you change the previous phone number with a new one. You can try and tell us the result, and if it does not work, you should try to recover this number in any way.