Not sure I completely understand the question but as far as infrastructure goes, it's probably half half old school telephone wires and fibre optic cables at this point. I think most cities have switched to fibre optics at this point but rural areas still have the old telephone poles. Some people on farms and in one horse towns will use satellite internet. There's also cellular networks but mobile data is unreasonably priced as far as I'm concerned and I'm not sure how people without wifi even manage to keep their apps up to date without breaking the bank. Although the majority of the country probably uses mobile data to access the net.

As far as social media goes, I get the impression that most South Africans prefer mingling with other South Africans. Which is kinda fair, there's 12 official languages here and quite a few distinct cultures, so I think a lot of people wouldn't get much value out of US and Euro dominated platforms like Reddit with walls of English text and Western references and in jokes. So places like Facebook and Twitter that try to keep you in your local bubble and circles make the most sense for a lot of people.