Mtn is *****ing our money

We took out a laptop contract in April 2023, but when received, the laptop it was not working. We then returned it immediately for a refund, and mtn received the laptop back. However they still debit the contractual amount every month on the laptop, despite us not having it. Every month we sit on the phone with them trying to sort this issue out to get the money back, but that cannot happen. It's been 5 months now and they owe us about R1000 for a laptop that we do not own. I have tried to escalate the matter but nothing happens.