Poor Communication

Hello, I had a Vodacom contract for internet which was capped at R149 per month. In January 2014 they deducted R1700 from my account. I called them so they can clarify why they deducted so much much. The lady I spoke to could not explain and when I asked them to email me the statement they did not. After two weeks I called them to cancel the contract. Now on the 22-10-2015 after 17 months I recieved a call from company called VVM saying that I owe Vodacom R7000, I asked the lady what this is for and she said its the money I owe Vodacom. And since I cancelled the contract in January 2014 they never called me to request the money and I stopped using thier serices since then. I am very upset about this treatment especially because they never told me this when I was cancelling and they locked my account after reversing the amount they could not explain, meaning I have never used thier data since then and will never use them again because I have been a good client to them and they decided to overcharge me