how can I fix my Thetford Toilet?

Please please help, our cassette toilet flush stopped working, so my husband checked the fuse of the toilet, which was fine, so we bought a new pump, my husband fitted the new pump, and it still does not work, and when we then checked the old pump, we found the old pump was working anyway, so we spent £31 pounds on a pump and that wasn't the problem. My husband checked the fuse again and all the fuses in the caravan and they are all ok, pump is brand new and fitted correctly and still no flush, so can anyone else please let us know what else it could be, thank you so much. Paula