Sue them and start filing interrogatories to discover what they are doing, if you are serious. But realistically this is - well, you were there, you know what it is. Generally there are three tiers of consequence for being scummy on the internet:
TOSsed out: your account gets canceled and you get banned off the service. The apocryphal example is getting your WoW account cancelled for botting, or scamming users for in-game gold. Another is exercising your "freedom of speech" on somebody else's freedom of press.
somebody sues you in civil court: the consequences are being ordered by a judge to do something, stop doing something, or hand over US dollars, to pay penalties or the other guy's legal fees. Consequences stop with that, and they can't take your money if you don't have it to spare. It's impossible to go to jail unless you really, really try, and generally, testosterone poisoning and a fair dose of sociopathy is involved. The developers of a WoW botting system got sued, and lost. Nobody went to jail but they probably had to file bankruptcy to sever the civil judgment and get their life back.
you commit actual criminal crimes online, such as threatening someone's life and safety, or defrauding someone of actual gold. At that point you get to meet the local police, get a free ride in a police car, get fingerprinted, arraigned, all that jazz like on Law and Order.
So when you get the "closed pending investigation" thing, it is almost always the first one. However, it's none of our business but you know what you did, so you know (or reasonably ought to know) what's coming. If you have no earthly idea what's coming, maybe you should have a lawyer guide you on use of the Internet.
Absolutely nothing about this is illegal (for their part). They have every right to close your account (freedom of the press belongs to them that owns one, Godaddy sells presses for $12 these days). Locking you out of your account creates a big question: why, and so they certainly must have the right to tell you honestly why.