Pethetic service and pay for system error

Early in September 2022 my wife called mtn to do a upgrade.She was offered a sim only package called MADE FOR ME XS.On the 12th September 10gig data,50sms and 150 minutes was received as per agreement.on 12th October 2022 only 1 gig ,50 SMS and 50 minutes was received.My wife then called and she was told that the package was no longer available and that the data ,SMS and minutes is all she receives and that the package was not available for 2 years and then a few months ago.She explained that that is not what she signed for whereby she was told that she can do an early upgrade for another package that had the data ,SMS and minutes that she says she signed for,for a fee of R200.Mtn says that there was a system error.So why must she pay for a system error.Service with the retention dept is pethetic who do not even want to retrieve the call of the day the upgrade was done.Both a consultant and senior manager insisting there is nothing they can do.