MTN poor service provider period

I was, correction I'm still an MTN contract holder, I'm Lindiwe Matebula number *** Had a 2year contract with mtn for which a monthly payment of R510, was made every month to mtn The contract ended on the 6th of February 2021 nd I decided to switch to a sim only contract which was supposed to cost R79 I receive an email from mtn saying that I owe a total amount of R1100 when I called one of the mtn 'service champion' Sqobile Ngidi she said mtn send me an invoice for an amount that was outstanding since April 2020,so I asked for an email to send proof of payment nd she said I must call tomorrow to send the proof She then sent me her email address nd I sent the proof and then she blocked my emails What kind of service is mtn providing to its users??? Is this one big **** where we can't get out of contracts, we are billed for things we don't know about??? This is really frustrating For the month o