Terrible customer service

I took out a Beam Me car tracker system which I wanted to cancel qfter selling my car, I was advised that I had to wait until it came up for renewal, and then cancel, else I would pay a penalty. I requested this and I go notification that my account would be closed on the 10th April when it came up for renewal. I received a bill at the end of April, advising that I would be billed again at the end of this month. I emailed MixTelematics and sent them their own confirmation that my account would be cancelled. They however still proceeded to take off another debit order this month for the full monthly subscription.