Mr Price unauthorised mobile sim

Mr price offered me a sim card as a way to thank me for opening an account only to realise today when i checked my statement that they **** instead they have opened a mobile contract for me without my knowledge which is ***** because i have no intention of owning Mr price sim im ok with my cell c contract,i want the mobile sim to be removed with immediate effect as i never authorise this and its ***** cant be paying for something i never authorised