Air Asia — family ticket booking

I booked 4 tickets for my family in one booking, 2 kids 1 senior citizen.
On the day of travel air asia counter people asked 250 per head extra to get seats together or else by default they will give 4 seats at 4 corner. They looted 1 k from family. What is the point of booking seats together in this case? Why customers have to pay extra after booking tickets, why separate charges for seat? Where are we going with this kind of policies, requesting travel ministries attention to regulate airlines.