Tired of bad service

It's sad when you will allow you good reputation to be run into the ground by one branch. Time and again we receive shocking service at this branch. Tonight again after waiting 20 min in the drive through queue, with only 4 cars in front of us we get told we will need to wait an additional 20 min as they have run out of chicken at 19h30 at night. Why do you have managers running your branches and do they not plan ahead? I'm done with your brand and won't buy there again.