Unhappy client

I'm really not happy with the service. I took out a month to month contract in October. I set up a debit order. I provided the agent with my standard bank account details which were verified and all. To my surprise, my services are suspended. I called MTN to enquire and I learned that the details were not updated on the system, instead they have my old account which is not active. This is unacceptable coz I gave out my account details, what was he doing with my details since he didn't update on the system. I'm very unhappy