Are you American by any chance? Air passenger rights are enshrined in EU law [1]. Asking a random employee to commit in writting for something that everyone knows that is mandated by law would just sound weird to them.

Of course the company may try to stall your compensation, hoping you will forget about it, but that's as far as they can go. After a couple of email exchanges they always yield.

[1] https://europa.eu/youreurope/citizens/travel/passenger-right...