The first two times I was on the phone with them, they explained that I could use a referral number as it was lost in the process of using it, even though I canceled. They said it was a mistake.
Finally, when I was ready to make a new reservation and use the referral number, it was expired, so I was back on the phone with them, and the representative then said that you do actually lose your credit upon canceling on our side. I told them that I had emails to show them that they were willing to give it back (as it makes no sense to lose your credit if you don't take the trip)
and she checked with a superior and told me that as I didn't know, (and also having been told twice that I had it), they were going to let it pass, but that it was a one-time thing.
I think they should put their guidelines on their website as I'm sure we're not the only ones this has happened to. I now know not to cancel when using my credit, but I'm sure that they will have more problems with future guests if they don't resolve it.