As Valve states, "VAC Bans are delayed." It is possible that you got banned for using some other hack before. There's an old case, which I would link if I find it any-time soon; stating that a player got banned after an year of using hack although he was not hacking during the time of ban. Once you're in the eyes of VAC test, you're pretty much fired. I myself used "ezfrags" once, and got banned after a month of using it; at a time that i wasn't using it.. Although I played a few games after using the external program, in which I didn't use hacks too.