Poor service and unprofessional staff

I'm still fuming about my experience today! I placed an online order for collection, and you guys called to say the chip machine was broken. Okay, fine, make the burger instead. But then you told me you don't have the burger or kids meal? And to top it off, the cashier's attitude was atrocious! She told me to go order elsewhere if I'm not happy. Unbelievable!

I'm writing to express my disappointment and frustration with the poor service and unprofessional staff at your branch. Why accept the order if you can't fulfill it? And judging me by my order? Not cool.

I'd like to speak to a manager, please. I want an explanation and assurance that this won't happen again.