It is a two step process. You need to call for the
DVC reservation and see if anything is available and it may be difficult to get anything at this time although often SSR is available that late. After that reservation is made you need to separately cancel the cash reservation. DVC member services has nothing to do with that and cannot make the cancellation. You have to follow required procedures for that reservation-- and I believe you need to make that cancellation in writing before the time you would incur a penalty for late cancellation.