Denied pre-booked seat/bassinet on Jet Airways int. Review on Jet Airways

I'm writing on behalf of my wife who along with our 2 month old baby had their most horrendous flight experience on Jet Airways flight 9W23 from Singapore to Bangalore on 6th October. Looks like they have double booked the seat 10E and my wife was denied it even though we had the records and confirmation from them about this seat booked. Jet Airways staff at Singapore airport continued to say that there was a problem with the Infant ticket but refused to give more details on the issue and denied offering any alternate seat/bassinet in the front row. My wife finally got a seat in row 12 and had to hold the 2 month old baby on her lap for the entire journey including the terrible experience of baby being hit on the head by the reclining seats from the inconsiderate passengers in the row ahead. I had also confirmed that the seat 10E was allocated to my wife under'Manage booking' on Jet Airways website before the travel. Having fully paid for the service and being denied it, I would like to report my grievance and demand a reply along with a compensation/refund.