Bad Service: Acting in bad faith

I cancelled my contract with MTN Woodmead shop on 16 January 2023: BA*** the last invoice was on the 25th January. Until received an account statement for a debit on 25 February because a customer service consultant didn't cancel it completely but placed me on a month-to-month plan, whereas i categorically said i don't need their services anymore. Their Customer Service acknowledging the error advised that i request a credit note, but my query is landing in deaf ears.