Dry Donald's

Very disappointed,my sister and I went to MC Donald's today to redeem our 50% off Big Tasty burgers from the MC Donald's app as we order the manager and drive through lady speak behind the window to each other but proceed with the order and accept our payment. As we leave we check our burgers to find them as dry as a dessert no sauce whatsoever ...we return to ask them where the sauce is and they respond by saying they don't have stock so me being upset I decide to remain calm and just ask them to put any other sauce on but they tell me I need to pay for extra sauce and the more I try to explain its not extra it's to replace what's missing the more they argue so I leave I'm very disgusted at the whole situation first they withhold information and expected to get away with this half service then they expect payment for their mistake and lack of sauces!