my account is not valid for use in the south african store. i must switch to the U.S store before purchasing..

See if this document helps. Change your Apple ID country or region, see https://support.apple.com/en-us/HT201389. Be sure and use the support options below if you have a problem. See this heading especially What to do before you change your country or region.

·      Spend any store credit remaining on your Apple ID. Learn what to do if your remaining store credit is less than the cost of a single item.

·      Cancel any subscriptions, including Apple Music, and wait until the end of the subscription period. 

·      Wait for any memberships, pre-orders, movie rentals, or Season Passes to complete, and wait for any pending store credit refunds to process.

·      Make sure that you have a payment method for your new country or region.

·      Redownload your apps, music, movies, TV shows, and books on any devices that you might use to play or read them in the future. That's because some types of content might not be available in your new country or region. (Learn what types of content and services are available in your new country or region.)

Use this link in the document if you need to View your Apple ID balance https://support.apple.com/en-us/HT202359

If you can't complete any of the steps, can't change your country or region, or you have less store credit than the cost of a single item, contact Apple Support.

You also can use Apple Support Twitter https://twitter.com/AppleSupportand

iTunes worldwide support to get help for text, chat, or phone support using this link https://support.apple.com/choose-country-region/itunes. At the bottom of your screen, use Tell us how we can help to select among support options.