Failure to honor Promotion

During the last coupe of weeks every time you placed an order you would earn credits this has been great until Monday 28 October, I get an email from UberEats stating I have R60 in credits to be used on a purchase valid for 7 days. I log into to my app to place an order and load my credits only for the app to say sorry this code has already been used before I then contact customer service who basically give the usual nonsense like you should check the expiry date of the promo code etc. After I reply to their email and attach the mail with the promo code showing everything they still say sorry nothing they can do and I must basically accept that they are not going to honor the deal. This is not how a promo works or how you treat your customers.