sorry to say, but i had no trouble to book seats, API and p/check in.
But here is how did it. get hold of your online or shop booking ref,,, HAS TO START with a letter then numbers , NOT YOUR ONLINE HOLIDAY BUT BOOKING you will see tne differance ,the one you do not use is two blocks of numbers and no letters
ie 1234-567890
Then go to thomascook airlines web site and not thomas cook holidays and go through ,,,,,, chose your seat.
whatever, you do stay with it on the airline web page you will achive what you want
from the 90 days before you depart
asthe THOMAS COOK AIRWAYS TAKE OVER YOU FLIGHT NEEDS...... DO NOT go on this site till 90 days if you go ahead of the 90 you will be refused