Bad service and not taking responsibility for it.

I took a Wifi router contract with Vodacom in May, since July it has not been working. Its been 3 months going back and forth with Vodacom about fixing the issue there is still no solution. The past 3 months a R600 debit order has been going off my account for data that I am unable to use. Vodacom is failing me big time as their loyal customer who has been with Vodacom since 2005. They are not giving me a concession about the months where i have paid for nothing instead they tell me they are investigating. Every time i call them the matter is handled by a different person. I now want to cancel the contract and they tell i must pay for cancellation but their device has not been working for 3 months. How unfair can you be to your clients, forgetting that you generate revenue from clients. Its like ****ting on your shade. I am very angry with Vodacom carelessness in dealing with client queries but the minute i dont pay my account they take me to credit bureau immediately. What should i do to cut ties with vodacom and retrieve my last 3 months worth of data that i have not received.