Method 1 aka replacement:
Works for: ANY pizza place as long as it's not a small-local business.

This one is very simple and you'll be able to draw some similarities between this method and multiple other food-related social engineers like Starbucks, vending machines, etc. Simply, a displeasing event with the company and you're going to complain about it in a well mannered fashion.

1. Order X amount of pizzas (phone or online, doesn't matter), preferred 1-2 but you will be doubling this amount
2. Once delivered call the place that you ordered from and complain about the pizza/pizzas you received
The pepperonis were very crispy and didn't tase well
The crust was unpleasantly hard
My pizza was lacking almost all of its cheese and it literally was unbearable to eat

Be creative and sincere about the issue you're having.

3. They will ask if you'd like another one/offer a "replacement" for said pizza/pizzas that you had an inconvenience with.

Method 2 aka coupons/vouchers:
Works for: Domino's, Pizza Hut, Papa John's, Blackjack, large pizza companies

With this method you will essentially be doing the same thing you did last time. Except:

1. You will contact the pizza place via their online support/contact form. Some have specific places for complaining / giving feedback so I'd use that one as it will have forms to fill out asking you like "when did you buy pizza", "how did you buy it"

For example, for Pizza Hut we'd go here:
https://order.pizzahut.com/site/contact_us

What would you like to tell us about? Restaurant/Food experience
How did you order? In-store/Walk-in OR Phone Delivery/Pickup
Date: I'd put anywhere between 3-7 days before the current date.
Time: Doesn't matter.
Store location: obviously whatever one is closest to you
Amount spent: 10-20 recommended
Did you share feedback with restaurant? No
Message:
(this will basically entail method 1)

Hello I ordered <pizza type(s)> on <date> and I've been a long-time customer of Pizza Hut (or alternative pizza place) and I never thought to have a bad experience with you guys or your pizza but unfortunately ate my hat. When I got the <pizzas> I noticed something was very off about how it looked, almost like a extremely sleazy amount of cheese that made the pizza look very unpleasant -- come to find out, the crust is rock hard as well. I didn't even bother attempting to eat it because I could barely put my mouth near it.

Things you could add in: you're very dedicated to ordering pizza on a schedule (x days of the week) and it's a ritual at home. You could also add in you EXPECT to be reimbursed but this is very zealous.

Just apply this to Domino's, Papa John's, any large pizza company and you should be fine. Obviously all companies will not have the same form but you get the concept.

2. The next page will have you fill out personal information. Fill it all out legitimately such as address and email. Address will be used to ship your coupons to and email will be notified once they have been sent out.