Give the offer 24 hours to respond ( "Confirms Instantly" doesn't always mean "instantly" )
If you still don't get the cash after that, head over to the offers page and find the "Support" link in the upper right
Find the corresponding offer you are having issues with and click the "Contact Support"
Fill out the form with as much information as possible, including any screenshots of "final pages" or confirmation emails as proof.
They usually get back to you within 3 business days.