The credit may still come, but here'e a couple of suggestions for the future.
1. Clear your cookies and temp files BEFORE you begin doing an offer -- whether it is a regular offer or one of the daily task offers. Also true for daily surveys, but you only need to clear the Temps/cookies before you begin doing surveys for a partiular survey site -- not before every survey you do in that site.
2. When you get to the final page -- whether it's the Thank you page or Congradulations, keep that page open for at least 10 minutes -- or until you see the credit in your account (I always have my account page open on another tab and refresh it periodically to see whether the survey/offer has credited.)
3. If after the alloted time (15 minutes in the case of the offer you did), if it has not credited, take a screen shot of the Congrad/Thank you page and paste it to your PAINT software. Add a fee comments on that page (I find it easiest to type the notes on a spreadsheet page and copy/paste it to the PAINT window) that described the offer, when you did it (day and time), reward amt; advertiser.
Save that picture as a jpeg picture with a suitable title that makes it easy for you to find. I generally titled it FCPOCmmddyy (FusionCashProofofCompletiondate) and save it to your shared pictures library.
4. If the offer/survey has not credited in a couple of days, send Support a ticket and attached the jpeg to the ticket and ask them to review the status of the offer. This may not get you credit, but it does give FC some information to work with and pursuing the issue with the advertisers.