One of my problems here as a former Team Leader was the inability to keep a permanently banned member banned permanently. I'd prefer not to give you any guidance on how one member got around his multiple bans but it is possible. Be forewarned, though, that as soon as your identity is discovered, the forum moderators will "Insta-Ban" without notice as many times as it takes until "you" get tired of "your game" (I am not accusing you - just "reliving" the nightmares from the POV of a moderator).
Having said all that, the lack of explanation is indicative of a MASSIVE violation of that forum's rules. At SitePoint, there aren't many that would generate an "Insta-Ban" but I can tell you that they are very serious and patently obvious. If you'd been "infracted" leading up to the ban, you were warned and sufficient accumulation of "infraction points" is sufficient reason to ban. Unfortunately, there are members who were only here to abuse the boards (and SitePoint members) - repeatedly. IMHO, it's better to be rid of that type of member than allow them back ... EVER.
Every can be a very long time. I don't believe it's a secret (moderators - edit if necessary) but there are two classes of banning: Permanent and two years. Give that forum a rest for a while and try again after things settle down.
Without being accusatory, find another forum (than the one you were banned from) and abide by their rules. I hope to see you around here for a long time!