MTN charging me for a cancelled account

On the 9th of February 2018 I called Mtn 808 customer care to cancel my contract as advised by a gentleman from one of thier stores in Durban west street that i had to call in 5 working days before the 14th of February 2018,I spoke to a Silvia Moshidi who advised me that the contract has been terminated and number migrated to PAYG ,after that call I recieved an sms advising that I was now on Prepaid, 4 months after cancelling the contract I get a call from one of thier lawyers stating that I have been handed over as I was owing MTN R544.01 excl thier fees which when I add thiers it comes up to R800 and some odd rands, I lodged a complaint they sent me a statement of account. On that statement I was invoiced this R544.01 on the 9th of February .Today I phoned 808 again spoke to a Sifiso ref : ********** 61 who explained to me that the Amount I am charged is the early termination fee which when I called for cancellation I was not advised that I will have to pay, Silvia only told me that the contract will be cancelled in 24hrs and she was so confident on the call I felt certain that she knew what she was doing and the cancellation was a success as I did receive the notification. Now why am I charged when I was not advised that there is some monies i had to pay if i cancelled that day ? I dont know MTN protocol , I dont work for MTN i feel I was supposed to be advised accordingly and decide on my own whether i continue or cancel the contract then pay . I dont have that kind of money , i did as advised by MTN employees they need to listen to those calls