Not allowing clients to cancel contracts after contractual term end

I have been an avid Telkom client for the past couple of years. I had 4 contracts of which 3 came to the end of their contractual term in March. I went in store to cancel these contract in Feb, where I was informed that you can no longer do cancellations in store and that all cancellations must be done via email. I emailed the required documentation on 19 Feb. I never received any confirmation from them. Up until 2 March I sent 4 follow-up emails asking for acknowledgement of receipt of the cancellations. I also phoned their contact center, who also informed me that the only way to cancel my contract is via the cancellations email account. They ensured me that the email would be received and actioned if I sent it to the correct email address. Long story short, I received an Invoice from them for April for an amount more than my initial contractual amount. My contracts were on discount, which now expired after the contractual term. I phoned the contact center again on 4 April. This time the lady asked me to send the cancellation request to her and that she would follow up with the retention department. I sent the email whilst on line, she confirmed receipt of the email and promised me that I would receive feedback within 24 hours. It is now the 8 April and I still have not received any feedback from the cancellations department. So now I am paying more for a product that I am no longer using and I have no way to cancel the product.