Breach of contract

Hi there. I have had a Vodacom contract for my cell phone and number for around 8years now. I have upgraded my contract as the years passed. Previously I were on a Smart L package from Vodacom. This contract I signed was for 250 Minutes/ second billing including 500 sms's and 500mb data. I agreed to that terms and signed my contract. My bill over the past year has been an average of R1300 monthly. This month I received a bill of R3700.I almost got a heart attack. I have been on the phone with Vodacom asking to investigate. Data bundles I bought were just gone and I received an sms that data bundle has been depleted and out of data bundle rates apply. I do not know why I got that message as my contract I signed according to my knowledge was for 250 minutes,500mb data and 500 sms's only.<br> I have then been told by Vodacom accounts that I used R2000 in data out of bundle because I had an open line. Where in the world. I have never heard of an open line before. I then went to Vodacom branch Secunda Mall and was also told that I had an open line and used R200 in data at out of data bundle rates. I then immediately changed my contract to a top-up which was explained to me clearly.