I dont think this is covered anywhere- happened to me at least 3 times past year:

1)What to do if you have paid for preferred seating, there is an aircraft change and you lose your pref seat and
you dont receive the refund automatically
2) What to do if you are upgraded using an e-upgrade , you have paid for preferred seating in Y and
you dont receive the refund
3) What to do if you use e-ups and pay the add-on to get J and are downgraded to PY
and dont receive the refund of the e-up credits and/or part of the add-on.

Many folks wont know/or cant find the link or place on the website to contact AC for these screwups as its kind of buried.