MTN Cancellation of Contracts/Numbers

We had a business and had phone contracts with MTN for a long time. In 2021, when my husband passed, I started to cancel all unwanted contracts and expenses. I have contacted MTN to which they asked me to email a letter on the business letterhead requesting to cancel services. To my knowledge, when a number is not used for more than 3 months, the number is cancelled immediately which happened to my husbands number. The cancellation did not happen and no contact was made to request documents. I have been debited for the said number for the past 3 years amounting to +/- R7000.00. I have requested MTN to refund this as the number was supposed to be cancelled automatically. Their response to this was " I was not due any refund". I still have 4 numbers with MTN and will be cancelling and moving to another network.