After purchase, I received a Booking Confirmation, reading as follows:

"Booking No: xxxxx
Departure Date: Sunday, 30 October 2016
Destination: Round the World Itinerary
Passenger(s): Mr JROBIN
Package: OneWorld Ticket
Flights including pre-payable taxes GBP xx x,xxx.00 x,xxx.00
Ticket: Cairo to ....
[ITINERARY}
...
No Outstanding Balance 0.00
E-Ticket Notice: Carriage and other services provided by the carrier are subject to conditions of carriage which are hereby incorporated by reference. These conditions may be obtained from the issuing carrier.

Air ticket rules and cancellation conditions
Cancellation conditions:
Before departure:
Prior to final payment, cancellation will incur loss of deposit. Once paid for in full, a 75% penalty per person is applied if the entire flight itinerary is
cancelled. Within 72 hours of first departure flights are non refundable. Within your itinerary, a 100% cancellation penalty applies for any
individual flights cancelled (ie these are non-refundable). For date changes and re-routes (ie changing, adding or removing a flight) please refer to
the date change and re-route conditions below. Due to the high cancellation penalty on these tickets, we strongly recommend that you take out
travel insurance when you pay the balance on your tickets. See here more details:
https://www.xx.co.uk/round-the-world-travel-insurance
After departure:
All flights are non-refundable. No refund value if part flown.[bolding added]
..."

In fairness, prior to ticket issuance, I did receive a Viewtrip reference so I could see the flights reserved, which is mostly what I was concerned about. After I paid, I also received a Booking Confirmation as a .xps file about 24 hours before I flew; I cannot easily read a .xps file, but it was sent because the TA's system was temporarily unable to generate pdf files.
I did not receive the Booking Confirmation email containing the booking conditions in pdf form until several days after I flew; the cancellation conditions were a total surprise to me, and not disclosed ahead of purchase, even to a customer who could read a .xps file.

Thank you for your suggestions.

I received a helpful note from Qatar Airways USA. Clearly they see that I should request a partial refund.
"Thank you for contacting Qatar Airways USA.

We regret that you are unable to complete your Round The World Trip.

Our records indicate that your ticket was purchased through a travel agency in the UK .

Kindly contact the issuing agency in order for them to submit your partial refund request via their accounting system.

Thank you for your understanding."


It is a big TA.

I forwarded the letter from Qatar Airways to the TA inviting them to request a refund, which makes clear that Qatar Airways is not unwilling. If I get a clear 'No refund available" even after that, I will try the measures you suggest.

Can or do TA's often add their own more restrictive cancellation policies to those of the carrier?