What I guess is that you may have WiFI at home and one of your family living together with you may have an account on the gambling site.
Another action that could have triggered the ban is an inactive account. If may be in time past where the user cannot remember but opened an account and for some reason either forgot password, email address or something else and then after some months signed up on the same casino with the same mobile phone, that would lead to very quick and immediate ban.