Disgusting customer service

I am so disgusted. I visited Burger King Uitenhage Eastern Cape on the 19th December 2022 at 6pm. We place our order and proceed to window one. This lady takes the money and we tell her we have a R50 voucher. She tells us it's too late as she already processed the order. We tell her we understand we'll take the drive around again as it's empty. She says we should rather use it another day. We then tell her the place is empty so we'll go around again. She advises we need to order and then she can load the order and we tell her that's what we want to do. We explain we wouldn't want to lose the voucher it's about to expire. She resists and tells us to use it another day. So to avoid frustration we pull away and hear her say "hayi suka wena stupid". How is this okay? This place has lost a valuable customer. Never going back again. Sis man.