KMM26835978I120L0KM - Honoring Seat Assignment

What was the itinerary change? Was your flight changed to a different
time/day? Was your flight changed to different equipment?

The explanation depends on what the itinerary change was.

you won't be getting any. Seat assignments are not guaranteed.

How would you feel if the airline charged you for changing your seats
from row 31 to 22?

If you read your contract of carriage you will see that seating
assignments are not guaranteed. Unless you paid for premium seats,
you are not owed any compensation.

Did you pay extra for seats 14B and 14C, or did you just select them?
31B and 31C sound like the same arrangement, just further back. There
are many reasons why seats can change, and it is a fact of air travel.
At least you weren't in 2D and your companion in 31C. It sounds to me
like a seat change was necessary and they did a good job of keeping
your arrangement and your party together.

You are not due any sort of compensation at all. Such a minor
inconvenience does not warrant the compensation you describe. That
request is ridiculous. Unless you paid $100 for those seats, you are
owed nothing in my opinion.