Calling has always worked for me. My free night certs never return on their own when I cancel a reservation (and I've tried all the workarounds people have posted). I just make sure the customer service rep knows a) this has happened before, and b) it usually requires someone else to intervene to detach and re-deposit the certificates. When I'm nice, it happens with one call. And a couple of the reps I've reached are aware it's a known issue.