Useless service provider

I sold my car last month, phoned my insurer to cancel my insurance as it is no longer my car. No problem @ all, even got a rebate because I already paid for the month up front. Phoned TRACKER to cancel my subscription to the service. Not cancelled. Phoned today to ask why. The responce I get: you have to give a calendar month's notice. This wasn't said to me at all, they deducted the money from my account this month again and the lady on the phone said to me that she can see that I requested cancellation on 04/05/2015, but nothing has been done about it. Now they come out and say that in their terms an conditions it says that you have to give a calendar months notice. Now they will do an \investigation"to see what happened. Very bad service delivery. Would I have gotten the same treatment if my car was ******? I will never make use of tracker's services again!"""