Will not pay for service not received.

Since last year I noticed that I don't receive my monthly data from iSmart any more. I phoned them to query the problem, and I was advised that they will rectify the problem within 24 hours. a Couple of days later I phoned them again since the problem was still not sorted. Still nothing. After several phone calls they said they will investigate and come back to me. Still nothing. I phoned again and was told once again that they will come back to me. Eventually after a lot of empty promises, over a period of more than a month, they still did not come back to me and I still haven't received any data, so I went to the bank and reversed my debit orders. They were quick to phone me to inform me my account was in arrears due to non payment. I then informed them that I reversed my debit orders since I haven't received the service I was paying for, for a couple of months and I would gladly pay if I get what I pay for. Suddenly I received my data and all was good, but not for long. The next month we were back to square one. Again I reversed my debit order. Last month 4 debit orders went through the bank and I reversed them again. I CANT pay for something I don't get. Last week I received an sms from them informing me that my account has been handed over for collection. How do you hand an account over for collection if you didn't stick to your side of the agreement? I am going back to the bank again today to reverse yet another debit order that went through to them a couple of days ago. I WILL NOT pay for a service I don't receive. I tried to sort this in a proper way by phoning them when the whole problem started, but as long as they get their money they don't care.