I am beyond livid with MTN!!!

I had a 2 year contract which ended in July 2015. I went into the MTN store in the V&A Waterfront during the month of July to ask by which date I need to fill in my forms to migrate to pre-paid in order to not get debited. I filled my forms in and was told it would be processed within 24 hours. A few days later my airtime was topped up and the debit order went off my account. I was furious and contacted the store and was advised that the migration was never processed, and nobody will take responsibility for it. I am still waiting on my refund. I then completed the forms again and was told the migration has been done. My phone was not topped up with airtime this month yet my f***** bank account was debited by MTN. How can they do this?!?!?!?!?!?!!? I AM LIVID!!!