I think you’ve answered the question yourself Bshankar, they only care about business class pax as they pay much more.
You don’t say your route or how much you paid but in today’s day and age with the most minimum of comfort and service given to Economy passengers due to the very low revenue the airline receives, it will be frankly amazing if you even get an acknowledgement. One Y pax more or less will make no difference to them at all I’m sorry to say.
My advice, don’t even waste your time or energy on it, just move on as you’ll get nothing from them.
Bshankar, read the above and listen to the wise advice from a gentleman who travels very heavily.
So do, often in business class.
My yearly spend is about 0.0000000006% of an airlines revenues – they simply do not care about individual customers and you will only stress yourself.