I can't buy backwards compatible games

So i tried buying pvz but it kept saying sorry we cant complete that purchase right now try again, so i did, nine times, but it didnt work, so i went to your website instead of the xbox marketplace on xbox one, same result, then i waited a day, same thing
happened on both console and pc, so i used my dads credit card, same thing, and i just bought a game called doom and destiny to test my card, it worked but pvz still didnt, why

:)