Heres some hints...
- your traffic method may violate their TOS... count yourself lucky to get even 1 signup.
- if the surfer does not log into the site, chances are you will not get credit for the sale.
- where is the surfer from? maybe their signup was flagged by the sponsor's fraud department or scripts.
If you know too much infomation about the surfer and when they signed up, I for one wouldn't be paying the amount most sponsors do per signup... and the join wont even nearly retain as long as the sponsor would like. If the sponsor isn't seeing profit after a while you will most likely be banned for attempting to de-frauding the sponsor's company too.
Friendly word of warning
If you are doing it legit, contact the sponsor first. This is not the place to be throwing around this type of infomation.