Signed a contract with Mrp mobile telephonically

Signed a cell phone contract with Mrp mobile and the agreement was am going to pay R79 per month and there will be a R99 for sim connection which I agreed on , but since that day I received my my handset Mrp mobile they have been deducting a lot of money when I call them to ask why they are just saying they will cancel it it has been going for two months now . Now I want to cancel my contract with them but the money is increasing every day this consultant says this and the other one say some thing deferent . I need Mrp to resolve this issue and refund me there extra money that they where deducting which we did not agree on .mrp mobile must get their things together