You also never signed a contract, so Niantic can do whatever they want, you can't complain, you cheated at a game, got caught and got banned, this is exactly how games should operate without fail.
I'd say Niantic are a month late to the party frankly, they should have implemented banning much sooner, server stability was an issue where botting was a factor (not the only issue obviously).
I've botted 4 accounts, I frankly got bored each of the accounts have a few 100% iv Dragonites, I've only logged into two of my accounts today, 1 is banned, 1 is not. Not all that bothered to be honest, I've only hit a gym twice, I don't play the game out on the streets (other than twice when hitting gyms from my car) and have never emulated to fake my gps other than botting, so for me the game has no value anyway.
the greed of people on making money on this game resulted on such action from niantic.
I hope niantic get hacked by anon or such tfor their game not to last anymore.