Still being billed 2 months after contract expired

I am still being billed monthly for my contract. It has expired after 24 months. I did give 30 days notice that I will not be upgrading. My number was ported to MTN and I've been using my new MTN contract since 29 Feb 2016. I want this sorted out immediately and I want ALL the money Cell C took back in my account PLUS bank charges I incurred due to Cell C' s negligence. This is absolutely ridiculous. See the email below sent to me by the Cell C customer service team, it clearly states that I cancelled yet I'm still being billed monthly after 2 months of canceling the contract ( please note that I didn't cancel this contract early, it expired after its full 24 month term). Email from Cel C customer service team: We hereby acknowledge receipt of your cancellation request. We are sorry to hear that you wish to cancel your contract with us. We sincerely hope that you would reconsider your decision to cancel and consider future deals to further enjoy Cell C benefits. Kindly note that your service in terms of your contract with Cell C will be discontinued on 29/February/2016 and your last invoice will be sent to you during the following month. Retentions Department Cell C - (PTY) Limited Buccleuch- Johannesburg