non-agreement upgrade

I had a contract with Cell C and never missed a payment until my contract ended, I got a call from one of the agents asking if I wanted to upgrade my contract which I rep**** no, then he asked if a month-to-month would be fine and I agreed, this means I could cancel at any time I only had to give them 30 days notice, I tried canceling my contract recently but they say I need to pay R283 because I agreed to an upgrade. I asked for them to send me a recording they had promised was initially available upon my request but now they are saying it's ******* for them to send the recording. The managers are refusing to speak to me and it does not make sense because I never agreed to another contract. I feel the company is de*****ing me and taking advantage and for this, I would not recommend cell c to anyone, this is a violation of my human rights, and I don't think I'm the only one they've done this to, please may you assist.