Given wrong advice by MTN retention department

My billing account is: BA***. My contract was coming to an end and with covid 19 having affected my family income negatively i phoned MTN to cancel my contract. I was transferred to retention and the guy gave me the amount to pay in cancelling the contract which was close to R4000. He then suggest that i can upgrade to a SIM only contract for R149. He assured me that starting from 1 January 2021 i will be paying an amount R149. To my surprise i received a statement on 22/12/2020 saying my next debit order will be R1137.27. Before this SIM only upgrade i was paying R879. My question to MTN is how can i say want cancel due to financial difficulty i am going through and end up signing for the contract where i will be paying more than my initial contract? My plea to MTN please correct this as your retention department misled me.