Steam will ban you and not tell you why

[gimperial]

3 days ago Steam banned my 250+ game/1000GBP spent account.

They refuse to say why, apart from saying I violated the Steam Subscriber Agreement - which I read, and I haven't.

Their notoriously bad customer service has been unhelpful, basically saying the same thing (you violated the SSA and your account won't be reinstated).

Even if I did violate the SSA, how is it at all OK to not be clear about why you're locking someone out of their account forever? I'm not going to make a new account and buy games because it would probably just get banned as well.