After a month still no success with request

My ****le contract ended in April. I called in the beginning of May to change my contract to pay as you go and I was told it would be done within 5 to 7 working days. More than 10 days later it still had not been done. I called again and was told it will be done within 2 days as the request is now long over the response time. This was 10 days ago and the new bill has been issued and its still adding data and nothing has been done. I spend half an hour at a time trying to get through to the call centre to speak to someone as the MTN stores no longer handle these matters. I am beyond frustrated as I feel I am wasting my time calling the call centre and nothing is being done. This month I will billed again for a service I no longer require. MTN customer service is appalling.