CW,
that is a very interesting experience, does not sound fun at all. Did you have any cramping or other PMS/AF signs. I would be frustrated too if I were in your shoes, it is hard to trust and believe everything the nurses tell you esp when you have a thousand questions and feel like they aren't giving you the answers you are looking for.
I only took Provera once and had a normal AF arrive the day after my last pill. So there is my two cents. I know that the provera does clean things out so perhaps that is all that was there, if it was a giant clump, maybe there wasn't anything left to come out.
hope that helps. I would try to call again and get more answers though or just get more clarification.
good luck to you and keep us posted