Apple ID problem

Dear All,

The last numbers of my phone number shown in my two factor authentication are not the right ones. Thus i can't receive the two factor authentication number.

And there is an iphone in my devices' list which is not mine. I have no idea how this device arrived in my devices' list, however i am pretty sure that the wrong phone number is related to this device which is not mine.

I can't use my icloud account to save my datas since then, and i can't find any solution to edit the phone number of my Apple id account and delete the iphone which is not mine from my list.

Can somebody PLEASE help me? I called Apple during few hours already and their response is that it is not possible that they can be hacked.... I have about 20,000 pictures that i cannot save now....

Thanks in advance !