I was contacted by people claiming to be from MTN selling phone contracts

I was contacted by people claiming to be from MTN selling phone contracts. I took it and a day later I decided to cancel it but no one at the store could assist with the cancelation. I called MTN and I'm being transferred from one person to the other. They confirmed an address that I lived in over 10years ago when I specifically gave them a new address. No one seems to be able to cancel the contract although it is on their system. I am very disappointed as this could be potential ***** case and no one seems to be able to assist