Ellen, seems to me at the least is to have them offer you a fair CPA (CPA on the high side) for all of your sign ups and move on. I know this is not the best of solutions but at least you would get some compensation for your efforts.
CPays is obviously in the wrong and should do what ever they can in a timely manner to correct this. Just my 2 cents. (is there a smiley 2 cents?)
Brian