What options do I have if I got far fewer airline points than what I was promised on chat at time on booking?

I had a ticket on Delta. I chose that miles be credited to my JPMiles account. I specifically asked the Delta chat agent how many JPMiles I would earn. He told me that I would earn around 19,744 JPMiles per passenger for the return trip (I have the chat transcript).
After completing the onward journey only 600 miles were credited. When asked, Delta told me to wait until the trip is completed (transcript available). Today, more than 6 months after the return trip, only 1,800 miles have been credited. I have lodged another complaint but Delta responds very slowly and I doubt that they will do anything.
What are my options?
I live in India and it was an India-USA return trip.
Update - I called SkyMiles and explained to them that I had already sent a mail with all the proof. After much persuasion they gave me two options.
- $300 travel vouchers each valid for one year.
- 20000 SkyMiles in each travelers account.
I choose the second option. Thanks for the help everyone!
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