Contract not upgrade for 3 weeks and receive 10 gb for R565.00 on the month to month contract

I had a 2 years SIM contract for a 10 gb and paying R250 pm with mtn and it expired on the 19th of August 2022. I took an upgrade on the 23 of August 2022 for a different product and I was going to pay R399.00 pm. On the 15th of September I received a statement from mtn and they advised me that I'm going to receive 10 gb for R565.00 pm. I called them on the 16 September they told me that to cancel the contract it will take 30 days and there were not convinced that it will be canceled. The upgrade that I told it was not yet finalized and they don't have the stock