Camera no longer shows up in Account

Hello, my indoor cam suddenly no longer shows up in my account. When trying to set it up again, a message appears that it has been setup in another account, so I cannot go ahead. This is really upsetting. Why would the camera just vanish from my account (that has two-factor authorization, no hacking), and I even cannot bring it back in. Does anyone have a clue to what can be done here? Thanks,Heiko