Terrible customer service and product

I have been a customer for +-3 years. Up and till recently when I called to check the unit and my current location which was not available. The call center agent said the unit might be faulty we made an appointment for the 20th Jan Nd up to date still hasn't resolved the problem and ii have been trying to cancel the service as it's useless can anyone assist me with some advice as I keep phoning the call center. All they do is put me on hold for a team leader until the call cuts. I would like to cancel the lousey service