I had the same thing happen to me. Get a hold of Microsoft support and they will either refund you or give you the items. I bought a bunch of minecoins and I got the same message as you. I was still charged for them as well. They were able to give my money back after a day or so.
My internet is fine and I purchased 1550 coins and this is what they do . I even restarted my Xbox 5 times.
I had the same thing happen to me. Get a hold of Microsoft support and they will either refund you or give you the items. I bought a bunch of minecoins and I got the same message as you. I was still charged for them as well. They were able to give my money back after a day or so.