Cartrack Very Poor Customer Service!!

I decided that after 5 years with Cartrack it is time for a change, first i battle to get them via their switchboard so i go online and get the cancellation form, even though my contract has ended after 3 years and i am on an month to month i see i need to give twenty days notice which i duly do, yet even though my service ends midway through the month i get billed for the entire month, when i query this i get the run around, excuse after excuse why they do not get back to me. From i were on holiday to just not replying to my emails. Low and behold come the end of the month i get billed again, all be it a lot less than my normal monthly subscription, i get billed again for a service that i no longer receive? I have never dealt with such incompetence in my entire life!!!