Sometimes sports bet predictions are leaked and with proper source you will get to know who's going to win. Maybe they found you suspicious as you are always winning on sports so they limited your sports bets. However your bets are fair and it does not involve any cheating but the information may come from outside. Maybe they are not sure why you are always winning on sports so they just put your sports bets on the limit.
The best you can do is wd all your money from their and try another trusted site.
You do not necessarily have to do something like that, as that would be considered to be a form of cheating, there are people out there which are so good at sport betting that they can in fact beat the casino at their own game, but if you do this consistently then it is obvious that casinos are not going to be happy about this and they will limit your account, so as you have said the only solution for the OP is to to open an account at another trusted casino and move on.