Beware of MTN "upgrade" packages

I have two MTN cell phone numbers, both on "month-to-month" packages. Last month I received a call from "Nisha" from MTN, telling me that these packages don't exist any more, and that I will be moved automatically to the new packages, which gives more airtime and more data. I said that is good, but if I will be moved automatically, why the phone call then ? She said it is just to make it official . . . She started rambling off the usual personal details, addresses etc, for the recording of the new agreement . . . and then quickly read "DO YOU AGREE THAT THIS IS A 24-month CONTRACT" . . . at which point I stopped her and rep**** a very loud and clear NO, as these telephone agreements are supposedly recorded. We ended the conversation with "I'm not interested in a contract", please keep as is. Last week the same "Nisha" phoned again, pretending that we did not have the previous call, offering me the same "upgrade", trying her luck again. I went to the local MTN branch, they confirmed that both my accounts are in order, and that there is no "new deal" which I HAVE TO be "upgraded" to. How can MTN staff get away with this nonsense, phoning customers saying that they have to upgrade to contract as their existing deals / packages expired ? Or is MTN telling them to do this ?