In your case, you can connect the Device to Gmail using 'Add Login' option in 'Settings 'and then always access it using Gmail.Â
Please use this forum for only feature requests...
About your issue, you are not able to connect to FB from your device account cos your FB already have another account linked to it. So, just login via FB... ERASE the current account linked to FB.
Trying to connect my game to Facebook, but it says it's already linked to another account—how can I remove that connection and link my current device account instead?
Kindly reach out to us at dev@dtmafia.mobi
Marco Agostinho