I had issues on the MS site a little over a year ago.
Needed to buy a new power supply for an xbox 360. The site would not take any of my credit cards - even though I could make purchases directly on the xbox with the same CC. I called them up and tried to place the order over the phone, still couldn't process card.
I know for a fact it wasn't an issue with the card as I was/am a prolific online shopper.
This said, more recently I have been able to order 2 sp3's and accessories via the ms store with no problem.