You do realize that Valve does delayed bans. If they detect you using some sort of cheat, they will not ban you right away, but generally within a couple weeks. This prevents cheaters from knowing what exactly caused the ban (especially if they are using multiple hacks). You may have gotten lucky and used a new hack before Valve new about it/added it to VAC. The only way to hack and ensure that you do not get caught is to create your own hack and share it with nobody so that way VAC has nothing to match it against.