You have 2 options .
Option 1 Go back and pull the offer and contact the third party and you should get the credits .Sometimes it takes a moment to get the credits awarded to you. So do this and give it about 2days to receive the credits.
Option 2 If after doing the first option you have not received your credits ,contact your credit card company and stop the payment . Since the full terms of the offer have not been met by the other party you have every right to stop payment . Just explain the offer to them and how you were shorted .You can always challenge any charge on your card as well as stop payments . You never have to take it on the chin . Hope this helps . :-)