Cell C debiting for a paid off account

I had a contract with Cell C, the contract expired and i went to the South Gate mall Cell C to tell them to terminate as i had no intention of taking up a new one with them. I was told by the gentleman there that terminations are not done in store i need to call a 3 digit number to terminate, i didn't have a problem with that process, my problem was that i no longer had the sim card, i had bought the phone for my mum 2 years ago, she has passed on i do not know where the sim card is as it was not her primary sim. 1. the consultants didn't care that i cant call the number from my sim which is not mtn they said i should look for someone on the network, i cannot be running around like a headless chicken looking for someone with a cell c number, 2. i went back again and explained to them that i cannot find a cell c number to terminate via phone call, they declined to offer me a landline phone to terminate and kept on giving me excuses saying that terminations are done during the week between 8 - 4. I feel that they enjoy taking my money every month for a phone i have paid off.