All you have to do is post the URL to the actual page on the end on the ccBill code like:
Code:
http://refer.ccbill.com/cgi-bin/clicks.cgi?CA=933495-0000&PA=1632535&HTML=http://www.britishslags.com/index2.htm
Though there could be another error are you using GET for ccbill_id AND site_link because if you are only using it for ccbill_id then the $site_link variable is being missed?