There is an issue right now with Facebook's login functionality. As such, logging into your Skullgirls Mobile with your Facebook account is temporarily unavailable.
Please be assured, your account has not been deleted and is still safe.
If your account is bound to multiple login methods (Google or Email), then you should be able to log into those instead for the time being.
We apologize for the inconvenience but we are working on this ASAP and should be resolved in the next few days.