Poor customer service and ********* call center agents

Very poor service. Ive been a customer with Matric Mix Telematics for over 5 years having a number of vehicles fitted with tracking devices. I had the service of one of my vehicles cancelled but they still kept this account active. Now the call center agents keep calling and pestering me to upgrade this unit, and apparantly Im still paying for the service. When I request them to cancel the service they direct me to customer service which is non existent. Please can someone contact me to cancel my service