Two things:
First: this is not an Xbox Issue, don't ask me how I know I just do.
Second: this issue is not only happening when you purchase ESO plus on the Xbox Store itself it's also happening on the subscriptions to ESO Plus purchased through your very own website.
So now that we have that out of the way, you need to fix whatever it is that's causing crowns not to be added to people's accounts monthly. It's irresponsible not to. Despite the ticket at the top of this page, this is NOT and Xbox One problem, it's a Zenimax Account System problem so directing people to the wrong place is also not the correct way of handling this emerging issue.
You need to look to your own billing servers to fix this, and more importantly update your sticky so that people who are getting the membership from your website but who are playing on Xbox are not directed to the Xbox support page when they are not getting crowns monthly!