MTN cancelled my free minutes without any reason or notice !

MTN called me last year in July 2023 to upgrade my contract with a great deal. It was on a month to month and included data and minutes. However, the minutes just stopped in April with no notice as to why. I have been calling MTN customer care but they cannot explain why its stopped and are blaming the rewards company but I am sitting with no minutes but getting billed for it! This is NOT acceptable.