Billed after account should have been closed

I am shocked and totally disgusted in the way CellC operates. Last year October or November i phoned cellc to end one of my contracts. When I checked my statement last month I was still billed for the contract. When I phoned customer service they told me that the account was not closed, and that they couldn't find any call that I closed the account. I am astonished at the way they operate. I told the agent I do not accept that, and that she should investigate and get back to me. It is almost a month later, I didn't receive any feedback from cellc what so ever. I am happy that my last contract is nearing its end, so that I can break all ties with this company. And will definitely never do business with them again, or even advise anyone that I know to take out a contract with them or even use their network.