Jet Airways — worst experience with jet airways again and again

I do not know why passengers are not allowed to select the seat free of charge. I was travelling with my husband from mumbai to portland usa and tried to select the seats 48 hours, 24 hours and even 12 hours prior to departure. We could not get a seat together for the flight which was available at no extra cost. The seat map showed all the seats at minimum $11 extra charge. We contacted customer care and they also said that seats are not available and we will have to contact check-in desk at mumbai (Source of travel) to get the seats allocated. We were travelling through a domestic connection which was delayed by 2 hours and there was no time left to contact the check-in desk but to go for immigration in mumbai. The jet airways ground support staff said we will be helped by staff at boarding gate.
When we requested the ground staff at boarding gate to change the seats they said all the seats are booked and they cannot assign us seats together. They proudly said that jet airways always overbook their flights and hence do not allow the passengers to pre-select the seats.
They gave us an option to request and swap the seats with our peer seat number if the other passenger agrees to do so.
This is ridiculous. We had to ask people to swap the seats with us during the flight which was very embarrassing.
Moreover, jet airways did not even provide any compensation for this inconvenience and did not even bother to regret this mess they had created.
I am never going to fly internationally on jet airways again in my life. They have worst service, uncomfortable seats in economy class, worst customer care.