Your order was wrong. That's annoying. But what you actually deserve is a proper answer, not a scripted brush-off. This page is here to help you get what you deserve: a letter that works, and what to do when it doesn't.
Leave anything blank if you don't have it. Only put in what's true, and only claim what you can show. A tribunal that spots one padded number stops believing the rest.
This decides how much you can ask for. Eating it counts as accepting it.
Example: you paid S$55 for a pizza but got one their menu lists at S$13. Enter 13. The letter claims the S$42 difference and cites their own price.
In-app chat is scripted and goes nowhere. Email creates a written record you can put in front of a tribunal.
Attach screenshots: the order page, the payment record, and the support chat. Send from the email address on your account.