I achieved my quickest, simplest, most pleasant customer service interaction yet with an airline by writing a letter explaining what they did (with transaction

I achieved my quickest, simplest, most pleasant customer service interaction yet with an airline by writing a letter explaining what they did (with transaction IDs, confirmation numbers, etc), and what they should have done. The situation was not entirely simple, and I was not looking forward to explaining it verbally to a rep. They sent me back a simple letter a couple weeks later saying they'd resolved the issue the way I requested and provided me the updated documentation. I'll definitely consider this approach next time something like this happens.