why have i been banned for cheating when i have never cheated

It's very rare that the system has banned you incorrectly.

You've probably been banned by a review of games. Suspicious activity that leads up to this.

EA will not ban you without solid evidence or a hunch that you're cheating.

In the very unlikely circumstance that you were banned incorrectly you'll have to follow their instructions in order to appeal this ban on your account (as mentioned above by one of the team members).