Credit One Fraud Las vegas Nevada Nationwide

I usually checked online 2/3 times a month before my due dates to keep track on my balance with credit one my credit line was only $550.00 I was always on time with my payments ea month with minimum of $25. I never had a problem with them Until May of 2016 I was going to pay and I noticed the statement shown I had paid $547. So I had a negative of $1.78 balance To my account (my balance was around $ 389. - 400. )I was confused I checked the next day it was temporarily suspended I called They had said possibly afraud and then they advised for a new card . couples of days later I was able to check again online someone had increase my limit from $550 to 750 and my balance was around $1200?? I called speak to a representative again they just don't make anysense and I ask for a fraud affidavit I live in Stockton ca and it shows I have transaction in Florida. said it will take 30- 60days for report to be mailed And I have to pay now my minimum payment of $64. I don't know what else to do when I call explain they aren't helpful at all I'm here just trying to build up my credit had been consistent w my bills now this happen