cartrak tracking your money

we were clients with cartrack for almost 4 years. another company contacted us and gave us a far better deal than cartrack and we accepted. i phoned cartrack and said i want to cancell they didnt even try to match the other companies offer just send me cancellation forms and said it would be cancelled after three to four working days. i let the other company come and put in the other devices and it would start on the first of August. i explained to the lady at cartrack that i dont want any other debit orders to go off anymore because we are sorted with the other company. this morning i found out we have a 21 day cancellation waiting period and that our cartrack devices are going to work until the 8August but my debit order will go off for the whole of august. tp me it feels like they are cheating if you put in a device in the middle of the month they let you pay pro rata but if you cancell and forbid it is in their 21 days of cancellation you will pay for service that they dont work for. beware guys read everything and ask quistion i did ask but they say 21 days is law and no one told me that when i cancelled