My prepaid plan was canceled

My prepaid plan is set to renew tomorrow but I received a message from Att that my plan is being canceled. Now I can no longer sign-in to manage my account or add money to it. Has this been a problem for anyone's else? Of course if it has, I suppose they wouldn't be on this forum. So anyone with knowledge of why this happened please let me know! I have not used my phone for anything illegal and I I haven't violated the terms of use.