Vodacom sucks

I have always been a happy customer of vodacom, but as of late I have been feeling very unhappy with the service that they deliver. It seems like my data is being eaten, like more than 3 gigs a day and they never give me feedback as to why this is happening even after I called in. I want to cancel a sim contract with them and now they want to charge me for the remaining months of the contract where I would not even receive that data. Vodacom is *****ing my data, I get 60 gigs a month and it does not even last 10 days and the data is so slow, so how can it even drain that much? I get less then 1mbs on a good day. I just want to leave this company, but they want me to pay for services that I will not be receiving, they inform they will call me back and never do and then sms that problems have been resolved when in fact it has not been resolved.