Cell C Deducting money from account for sim

I app**** for a cellphone contract from cell c. The next morning I emailed cell c and the sales rep saying I have to cancel. The sim arrived from the couriers, unfortunately I signed for it. the contract was cancelled in the meantime, no phone delivery. I get deducted monthly for the sim. still sealed in the couriers delivery box. Apparently they cannot cancel the sim, because I signed for it. Still sealed. only way they can cancel it is by me paying for the whole 24 months of the contract. The contract was app**** for in may, sim not yet been sorted and not been used