No Service

I have a cell c data top up contract. I got a call to upgrade my contract I was offered a mi fi. So I took up the contract not knowing they changed my contract from top up to open line. I spoke to a consultant she told me I will have tp wait two days for someone to get back to me.Last night I get a call to say I owe 2700.Im supposed to be on a top up. Its supposed to stop once my data has been used up. How can I be moved to an open line with out my consent?I wouldnt recommend Cell c to anyone. The staff is *********** and rude.