Why cant I use my reward points in South Africa

Because South Africa is not on the list of regions where Rewards is available:

"Microsoft Rewards is now available in the US, UK, France, Germany, Australia, Canada, Ireland, New Zealand, Singapore, Italy, Brazil, Mexico, Spain, Sweden, Norway, Belgium, Netherlands, Japan, Hong Kong, and Taiwan"

https://www.microsoft.com/en-gb/rewards/faq#

Hi, I hope you're doing great out there. I am an Independent advisor and I am here to help you in regard to your concern.

Just a friendly reminder though that for Microsoft Rewards concern there is a dedicated team that handles them which is the Microsoft rewards team.

To help you, please visit this link and click on "Get Help":

https://support.xbox.com/en-ZA/help/account-pro...

I completely agree, we dont get the rewards program here in South Africa, yet i get the reward emails and even have about 100 reward points from some where

It could be based on region lock? perhaps thats why, we cant download it here in South Africa either.

Hello GlaringLion3637,

Since your Microsoft Account is set to the South African region, you cannot register into the program. South Africa is not a Rewards eligible region. If you have just recently moved from South Africa to a different region, keep in mind that it takes us up
to 96 hours to receive and process new information.