My account was banned when I wasn’t cheating

Hello, recently I received a email saying that my account was banned it put me into a bit of shock becuase I don’t know how I got banned. I kept reading the email until it said your account has been blocked from online for cheating which makes no sense becuase I never cheated on this game, I remember my freind calling me a couple days ago asking me to play becuase he saw me online I told him I was in bed and he said I was playing with my old username which was Funkymonkychunky my current username is coreyz2005 I thought he may have been just playing on my account and trolling me, the next night I logged in to play some ranked and I noticed I was silver 3 all of the sudden when I was bronze 4 the night before which made no sense. Then today I received the email and it all made sense someone must have hacked into my account to get me banned. If I could please have help it would really be appreciated becuase I really love this game and I don’t want to have to start over and lose all my stuff