Disssapointed in Checkers 60, delivery integrity and promotional discount that they didn't give

I did order on the 4th of Aug for delivery on the 5th of Aug between 8:00 - 9:00, some items, order ***A, total of order R763.90 after my promotional discount. When they delivered on the 6th the delivery guy claimed that he couldn't get hold of me, and returned the items to the store and cancelled the order. I immediately when I see the cancellation, re-order exactly the same items order ***A. When they delivered they charge me R893.90, meaning that they didn't allow my promotinal discount. Since then I phoned weekly their customer care help line, every time I have ti repeat the issue, ref no ***8, still till today they did not credit me. Everytime they promise that the money will reflect in my wallet still the same day, as this morning at 8:30 still not the case.

What do I need to get this resolved, or must I just accept this is the type of customer services I can acpect?