My experience with CX has been great. I would think about a few things:
1) You are running for just such a short time, there could be something off with CX's pixel and the advertiser's thank you page.
2) The advertiser could be scrubbing the leads somehow.
3) eAdvertsing could be over stimulating the numbers for you. Maybe they have a larger margin so they can overreport and want to grab you and keep you on board.
Good luck!