Unauthorised debit order

This company has been debiting my account for over two and a half years without my consent. I spoke to my bank recently and they said that it seems like a ********** debit order because the amount that they debit varies every now and then. This means that if I put a stop on the debit order, it will put a stop to one amount, but they can then carry on debiting another similar amount. I have tried to get in contact with them multiple times and each time they avoid my calls and say they will get back to me but they never do.