This is due to an undersea cable that broke. It is set to be repaired by 4 April.
An undersea cable that connects South Africa to a large part of the rest of the internet broke (again) over the weekend. The result is that some South Africans might experience very slow internet speeds, especially when trying to access overseas websites. This comes at a bad time, seeing as most people are working from home during the nationwide lockdown. According to the government, the repair of the cable will only take place on the weekend of 4 April.