Needing an App not available in my region

You can't really resolve it other than moving to S. Africa. Apple's media terms of use limit availability to your country of residency, or "home country". Even if you wanted to change your country settings to S. Africa (and thereby jeopardizing items you have from the UK) you may find you need a S. African credit card to do so.

http://www.apple.com/legal/internet-services/itunes/uk/terms.html

Click on the link and read how to "Change your Apple ID country or region" - https://support.apple.com/HT201389

You can contact the app developer and request they make the app available in the UK.

How to contact an app developer - https://support.apple.com/HT207959 - "You can find contact information for app developers using your iPhone, iPad, iPod touch, Mac, or Apple TV."

Probably others have done what you want to do.

If you're using iCloud services with a lot of your data it should reappear but you may have to do a bunch of tapping to answer questions if you want to merge, etc. Not that I have done what you want to do so can't speak from experience.

'Welcome!