Definitely keep trying. We're taking a last-minute trip 5/14-5/16. I called yesterday (5/8) to see what kind of ADRs of any type I could arrange, (expecting everything to be gone) and while I was on the phone, just about to hang up, the CM informed me that a cancellation had come up at that moment for Le Cellier!!! (Le Cellier was one of several I had asked about - originally told sold out). So, we have an ADR for 4 for dinner at Le Cellier, booked on 5/8! Keep calling!
(BTW, my cell phone plan allows free evenings and weekends all over the US, so that's when I call to avoid long distance or per-minute charges.)