I insist on receiving payment before providing pizza
Why do you require advance payment?
I find it necessary.
It seems like common sense to pay before getting what you bought. I expect most places have a similar policy.
I will punish people who wants to get pizzas before paying and I will be angry at them.
I wouldn't punish people just because they want the pizza before they paid as they may not be aware of your rule. If you really require payment first, then just say so, instead of immediately being angry at them. More people need patience and understanding nowadays.