I have been having an absolutely horrible time with this myself. I too believe it's a scam and would like to leave a complaint. I also purchased something that I would not have purchased if not for the cashback that was promised and I've been struggling to receive it for over a month now. I opened support requests twice and both times had it closed without resolution. Both times the representatives requested the same information multiple times, which was provided multiple times, and then they closed it, after requesting it again, though it was provided to them through image, invoice, order number, name of the company, price of the item, date of the purchase, etc.
This has been the worst experience I have ever had with customer service in my life and it's a shame because Microsoft usually presents itself as such a respectable company.