I've used this site to purchase Xbox live subscriptions multiple times without any problems.
My recent experience with Xbox live.
My Xbox subscription recently expired and i didn't realized the payment card attached to it was no longer valid, because I've been using this site for prepaid subscriptions. Microsoft put my subscription into "suspended / past due" status and Microsoft will not allow you to use a prepaid subscription code if your account has that status.
You have to purchase your membership with a valid credit card from Microsoft directly, before your account can be removed from "suspended/past due" status.
I've purchased two memberships today:
Microsoft -- 12months $63.00
cdKeys ----- 12 + 3 months $55
I don't have to worry about renewal until October of 2019. lol
Lesson learned:
purchase and use the discounted membership prior to your subscription expiration.