Sadly, this has happened many times before, especially to out of work pilots, who have not worked contract overseas.
There are sizable monies held in escrow or on account, if you know where to look for it.
This company must have an account with Gulfstream and RR as well as Jeppesen etc.
Find out who legally owns the aircraft - is it a bank or a leasing company?
Who was the flight planning company?
Who was going to handle the aircraft and arrange permits etc?
N927GA was deregistered by Gulfstream for export to India.
FAA Registry - Aircraft - N-Number Inquiry
This aircraft is not currently registered in India
Active Aircraft Register Enquiry
And is not currently approved for charter
http://dgca.nic.in/firms/Western.pdf
I would suggest that you write up all of your expenses, attach a copy of the written agreement and copies of your expense receipts in a nice folder.
Write to the owners, by registered mail. Be polite, just ask for what was owed and next time, get it all in writing.
If you do not get a response or a refusal to pay (actually very useful, because the return letter becomes an admission that there was an agreement):
File a lien with the companies involved and send a copy to the registered office of the company that owns the aircraft.
Putting a lien on any one of these well funded accounts usually gets some attention very quickly.
You can also file a complaint with the aircraft registry. Indian, Bermuda, UK. IOM?
As a prior contract pilot myself - I have to also ask - did you have an Indian crew Visa?
Whose registry was it? The DGCA would have issued you with a flight crew license validation if it were an Indian registry. This would have been supported by a letter of sponsorship from the operating company and would therefore go towards proving that you were in the country for a legitimate reason.
I am assuming that you have a written contract? Otherwise, you were on vacation in India, with little formal recourse available to you.
If you go off flying contract again; never purchase your own ticket or book your own hotels with your credit card and always demand an advance. It just isn't worth it and any reputable company will not have any issue with these requests.