Cancellation

Bought a power supply through Vox, paid it off for the agreed upon time. i have been trying to cancel this contract for months yet i am still getting statements and being charged. I was told after that I have to pay a cancelation fee which is absolutely ridiculous. How does it make sense to still charge someone every month for an item that is already fully paid for. There is no longer any services so how can vox still charge it makes absolutely no sense. There is no feedback/ response from them. The product is working fine but the service is pathetic. would not recommend them to anyone