Please unban.

I recently started playing CSS again and first servers I tried to join were KSF Clans servers. After selecting the server a box appears which tells me that I am not on the server whitelist. I don't remember why or if I got banned. I used to play in KSF Clan Surf servers some time ago, but I don't remember getting banned. Please unban if there was no reason for banning me in the first place.

99.9% sure you're trying to join a private server. Try joining one of the servers from here: http://surf.ksfclan.com/connect/