Poor service and misleading information

Matrix telematics- I spoke to an agent and we agreed on the R99 subscription but to my surprise I was now paying R150 which was not part of the agreement between me and the agent. I am now not even using their services but I am apparently owing them over R1000. I am very unhappy with their service and I am receiving sms's and emails that I will be listed on credit bureau as a slow payer. How am I suppose to pay for an amount that we did not agreed on. Thank you