You can contact TelkomZA on the forums. Please just note that it may take more than a day for them to respond since you can imagine they are pretty busy being understaffed.
Also include the following information in your message to enable them to report your problem to the relevant engineers as quickly as possible:
"Gonna need your address and LTE service number, if you could confirm GPS location that will also be helpful, can then request intervention"
As a bonus I also sent sample speedtest results showing the problem and also included the Cell Id of the tower I am connecting to.
Hope it helps