Lack of response by Supplier, Inaccessablity

I have a contract with MTN provider which I took via Nashau Mobile, last year I filled in a form to cancel this contract, however 2 months later my kids was still getting airtime and when I called and asked about the cancelation, they said the lady that originally took my call has left and the paperwork was not processed. I then requested to please proceed with the cancelation and migrate to pre paid, Again this did not happen, and when I called a month later, they told me that MTN is now taking over the contracts and I must cancel via them. I called ***, but cannot get thru to them for customer queries, Subsequently on Monday 06.04.2015, I finaaly went in to the store to migrate , they then told me they cannot do this and it must be done telephonically, I have spend a total of 20 min at a time holding on listing to music, and finally had to put the phone down. So far I have called 11 times without success. My frustration is growing at the lack of availibilty of anyone that can assist and the people that i do speak to just shrug their shoulders and refers me to customer service again. I have even threatened to stop the debit order, to date no-one came back to me.