After reviewing many reports of in-game cheating, we have started taking action against players taking unfair advantage of and abusing Pokémon GO. Moving forward, we will continue to terminate accounts that show clear signs of cheating.
Our main priority with Pokémon GO is to provide a fair, fun, and legitimate game experience for all players. If our system has determined that you cheated, then you will receive an email stating that your account has been terminated.
If you do believe your account has been terminated incorrectly, you should report it to the Pokémon GO Help Center:
The Pokémon GO Development team