Customer care does not work

On the 9th March 2016 I converted my MTN contract to pay-as-you-go or prepaid. I was subsequently debited for the amount that differed from my invoice. When enquiring at two different MTN stores was told they could not assist me as I am on pre-paid and they need to contact MTN. The store assistance left the phone ringing on the table while attending to other clients. I waited for an hour for someone to answer the phone then left. I then sent an email to the customer care and was informed to phone there 808 or 173 numbers. There was no option on the call centre to select to attend to my problem as the 173 number is for pre-paid and my query was for a contract and the 808 number could not assist because my number was now a pre-paid number. I once again emailed the customer care asking them to assist. I received an email stated the difference is the usage for the 9 days usage in April. I paid the invoice via EFT and requested an invoice for the remaining amount and was informed that I would receive and invoice once the debit order was processed. I have now been debited the full amount again and my emails are not being answered. Am I not entitled to better service and to an invoice before being debited for the payment amount?