Terrible Customer Service at McDonald's

Greetings I am a customer who is very angry at this moment, I am at a restaurant and am recieving the worst service ever. I tried to redeem an offer from the app and the manager (who didn't identify herself) blatantly refused to accept the redeem voucher from the app she claimed I can only buy one item whereas the app allows me to buy more... I explained to her that I need both items on offer today as I can not travel to a McDonalds franchise everyday to redeem an offer, I go to work during the day and the offers can only be redeemed in store they are not available for delivery . I had already redeemed voucher and instead of serving me she stood there arguing until the offer expired even though I offered to pay the balance as it is a half price order. This rude manager (who I can identify ) saw that the offer is already redeemed but instead of ringing the transaction she shouted at me in front of other customers and the cashiers telling me that she told me she cant allow me to redeem 2 vouchers I mean it's my money, my app offer paying yet she is refusing , this is extremely poor service and I will be exposing McDonald's for misleading customers. The store number in question is # ********** at Pan Africa mall. The offer I tried to redeem is for a big tasty at half price which I really wanted but now I'm sitting at this resturant only having ice cream but I'm hungry. I really want this big tasty at half price or else I downloaded the app for nothing and McDonald's is lying to customers and wasting their data and time. I mean I won thw voucher by using data to play on the app but now I didn't even enjoy the meal I wanted.