I've experienced such problem with being banned from a certain server, where I have never played before.
2 months ago in de_dust2 there was a latvian cheater, he had the same IP as me. We both got banned. I never knew, who he was, though. As to mention, back then I was still a non-steamer.
As for the steam ID -
Free downloadable non-steam CS might surely have this issue (same ID's).
There's also a steam ID changer.
So I suggest to unban this guy, since he's not the only one suffering from this problem.
BTW guesswho, for some time I thought you were Ryan. I've seen him in dd2 only and he was a quite good fella.