Boxes issue

I bought the 3 medium pizza deal which comes in one box. Me and my family ate 2 of those pizzas and when my husband asked for a.seperate box to put in the last pizza because we didn't finish the last one, he got a ugly answer and when I went the lady said they dint have medium boxes and everything was counted so I should take my pizza open as is. How can they not have medium pizza boxes if they sell medium pizzas? I don't understand I had to leave with an open pizza which is gonna be cold when I get home.