Air India — Seats reserved but not allocated as shown per booking

Dear Sirs,
I had purchased travel tickets from Delhi to Frankfurt and back on Air India thru Booking.com, I was given option to block seats of my choice which I did and paid 2500 person per sector (3 passengers I paid total 15000 for return journey) I was shown seat options whilst booking and I blocked EXIT ROW Seats by paying 2500 for each passenger each sector. To my utter shock and disbelief, and upon boarding the aircraft I realized I was not given seats as promised as such I was charged 15000 Rs fraudulently, Air India, refused to honour and Booking.com refused and put the ball back to Air India, can you help with this matter, thanks Pradeep ([protected]@gmail.com)