Pathetic service with online purchase

I have been struggling for months to have a contract cancelled in which I received a laptop which didn't want to power on. All the while they have been deducting the monthly debit order. Eventually, I got fed up and stopped the debit order. They couldn't jump into action quick enough to collect the laptop at my house. Long story short, it has been an additional 3 months, and I have been listed as a bad payer and am now unable to purchase another laptop due to this. The contract has still not been cancelled and they are still deducting the debit order monthly. I am livid at this pathetic service. I will never be purchasing anything through MTN again, after being a lifelong customer of theirs.