Bad customer service

I went to MTN at Giyani on the 14th of February for a contract (router) I paid R419 for activation but from then till date the router is not working. I went to the store 5 times for help with no solution even now I'm calling them they are no longer taking my calls. I'm told to call 135 but I paid at the store. I'm now far and I received a bill to pay again for something which is not working