I am so angry with mtn

Last year November I was advised to contact the mtn service provider for cancellation of my contract that has come to an end which I did and never received a reference number come February my cell phone was not working as the service provider mtn, disabled my sim so I had no choice but to go to the store to pay up an amount of 1200 and same day my phone was working they even upgraded my contract without my consent mtn upgraded my sim with 2 gig and 25 minutes all networks however I asked mtn to cancel as I was so not happy with the upgrade I went again to the store they gave me email address to send and email to cancel the contract I did. Until now Mtn is saying I am owing them amount of 700 to cancel the contract mind you my cell number is not working I cannot dial out .I am so not happy with the mtn and their service and this is the only number I am having