Can't redeem points because I can't add a phone number

First of all, I'm being sent around in circles on this topic now. I've contacted both Microsoft and Xbox support with both telling me to contact the other as they will know the best way to deal with the problem.

I'm trying to redeem Xbox Rewards points. However, when I do it tells me that I need to add a phone number to my account (which is already there). I go through the process of adding my number, I receive a code, I enter the code and then I get the warning message "There's a temporary problem with the service. Please try again. If you continue to get this message, try again later."

This has been going on for months.

Microsoft Support Request 7032769452

:)