Bad customer service from Netstar

I cancelled my Netstar on the 9th of January. I have repeatedly sent e-mails and spoken to people that promise that they will sort my complaint out. The debit order keeps on going off although I do not own the car (or the Netstar) anymore. I stopped the payment from my side since Netstar is not assisting me at all. Now the collections department is phoning me to say I have an outstanding amount. I am fed up and do not know what to do about this anymore.