Cancelled contract being deducted from our bank account

We signed up for a LTE router in July 2017. August 2017 we had to return the router as we were not allowed to configure the router.

We received two invoices and credit notes. Then 1 October and 1 November we are debited for invoices that were not credited.

Phoning Vodacom is an exercise in futility. Calls are simply dropped or you are put through to somebody else or asked to rate a call when no assistance was provided.

Can you please sort this mess out. We cannot be expected to pay for a contract that was cancelled and equipment collected months ago.