Ignoring my cancellation

A tracking device was installed in my Honda Accord over 3 years ago - the car was sold over 2 years ago. The contract was cancelled with Netstar. All good, you would think - WRONG! Three months ago, out of the blue, money is deducted from my business bank account. NETSTAR have decided, on their own, that I owe them money. THIS IS TWO YEARS AFTER my car has been sold! I phone Netstar, explain everything, they tell me that the contract will be cancelled and the money reimbursed. I, in the meantime, contacted my bank and requested them to reverse the debit order. NETSTAR then deducted a DOUBLE payment last month, so I thought perhaps I should leave it and then they will reimburse me. WRONG - they deducted yet another double payment this month. I have sent THREE separate emails to them, so that I have a paper trail and I have not even had the courtesy of someone coming back to me. I have in the meantime notified my bank that this company is now **********ly taking money from me. The bank has returned my money but NETSTAR have not contacted me. I want to know that they are not going to try to take any further money from me and that they have in fact made a mistake.