You'll dispute the AMex charge because it's not what you paid for?????

Your charge is the right of passage from point of origin to destination. Which is what CX gave you. There was a seat. At least you didn't have to stand - because that would be a breach of contract. You got to sit down... even if slightly uncomfortable, from start to end.

If you were really that uncomfortable, you could have very well exchanged seats with someone in J who would have been more than happy to sit upright and enjoy all the perks and services just being in F class.

I wouldn't believe that CX would have let you go entirely hungry. They must have fed you something...

I agree with christep, that services relating to meals and inflight duty is beyond their control. Blame ground catering.

And you got upgraded from J which is what you paid for.. for better personal space in F even though there were some service issues...

You may try writing...to CS.. but trust me, they would know that you got the upgrade! So write fairly..