Deeply frustrated with MTN accounts department continuing to charge me after my contract ended.

My MTN contract terminated on 30 January after at least 27 years as a customer. I contacted them in November and was told I should confirm my notice one month beforehand which I did - and then again on 30 January. I got confirmation that my number had been transferred to Pay as You Go and then ported my number to Standard Bank mobile. I was debited beginning February which I accepted as apparently accounts are charged in arrears. But then again I was charged beginning March. I instructed my bank to reverse the charge. But I cannot reach MTN as I no longer have an MTN number. I have been to a store (they told me I had been charged a cancellation fee - but how is that possible), I have tweeted, I have emailed and tried to call with no success. Today I had an automated call to say that I owed them money and decided to use the opportunity to speak to a consultant but nobody answered. It is impossible. I will continue to reverse charges but have no idea how I will ever sort this out if I cannot speak to them and they don’t reply to my attempts to reach them.