Hoping that the vast knowledge bank of FT can help me find the answer here!

I have an upcoming Finnair flight, with ITM-NRT-HEL operated by JAL.

I'm desperate to reserve a window seat, particularly on the NRT-HEL sector as it's a 10 hour daytime flight - there's no way I want to get stuck in the middle!

Finnair online doesn't allow me to select a seat for this sector, so I called them and they said they couldn't help and so I should contact JAL. I managed to find my booking on JAL.com but again it didn't allow me to select a seat, and so I emailed JAL using a contact form through their website and they told me they couldn't help and I should contact Finnair. It's getting a bit boring now!

Any ideas how I might be able to do this, does anyone know of a magic phone number or e-mail address? I don't have One World status.