Do you mean you are not able to sign in using a remote dial in to Comfort , or your local telephone?
ADSL or fiber may affect DTMF detection when calling in from a remote phone
It should not affect using your local phone to sign in to Comfort. try disconnecting the incoming TEL IN to comfort and signing in with your local phone. The phone should say "Phone Trouible Please sign in" Then enter your coide and # key