Being Overcharged by Telkom

Telkom has the worse customer service, it is lacking drastically. I app**** for a sim card contract in 202 and the agreement was to pay R99 monthly as if included 20gb anytime data and 20gb night surfer. I was never charged that R99 but instead they were over charging by R800 stating that it’s because of a spending meanwhile I have never agreed to it. They also kept on blocking the sim card stating that I am not making payment. I have never been charged the agreed instalment but they have been over charging me instead. Telkom has caused me pain and suffering so I would like to be refunded