KFC
Drive Through service very slow

I went to buy some food in evening KFC drive through, we waited for our food for nearly 30 minutes. I asked the lady why the service was very slow, she wanted to close the window without answering me, i insisted to speak to the manager in charge. He just looked at me and continue with his business like as if nothing has happened, no apology or let alone an answer to my question. I have been to other KFC drive through, their services are very quick and i have noticed that this particular KFC you wait for your food forever.