Cannot return/swop damaged goods

I recently signed a 24 month uncapped LTE contract with Telkom. When I got back from holiday, the router was not working anymore. I went in to a Telkom shop to swop out the modem for a new one. The lady told me they cannot do repairs or swopouts in-store. They gave me 2 numbers to call, which led to 2 new numbers to call, which lead to dead ends. I have tried contacting Telkom via the website chat, but they keep telling me they cannot help, and provide me numbers that keep ringing without answer. The lady in the shop also said that I cannot buy a new Modem. So they cannot repair or swop my modem out. And they also cannot sell me a new one. So I will be cancelling my debit order until I get a new modem. Currently I see no way to contact Telkom about this issue.