Difficulties Cancelling a Matrix Account

We have been trying to cancel the tracking for one of our vehicles that is currently not on the road. When you dial the switchboard number and request accounts, they (accounts) advise that they will sent you to cancellations. Unfortunately the phone does not get answered from thereon. We tried this several times over lengthy periods to no avail. We then had to resort to cancelling the Debit Order(D/O). Matrix now insist that we pay for the Debit orders that were not honoured by the Bank. We have refused to pay these. However in the last 2 months, they snuck the D/O back after changing the amount slightly (with FNB D/O are stopped for 12 months). Thankfully the Bank reversed them. This has become a very ************ business.