I've had a weird experience with Qatar customer service as well. Basically during covid you could get a full refund if you cancelled or rescheduled your flight. I wanted to reschedule my flight to another final destination, the support agent said they couldn't do that, but could issue me a voucher, and hold a reservation for my next flight. All I had to do was pay that flight with the issued voucher.
However they failed to even send me the voucher within 24 hours, so when I called back, I was told the flight would be an extra US$3,000.
I tried to explain the issue, that they never send me the voucher, and due to that I would be on the hook for extra costs? The support agent was totally uncooperative, and just kept asking "what would you like to do". Turned into a bit of a shouting match.
In the end I had my flight cancelled, and a voucher was issued straight away.
I still don't understand why they couldn't just look at their own logs, realize they actually didn't send the voucher, and just book me on the original flight. Or why the first support agent couldn't just use my voucher to pay for the flight.
This was also a business class flight, so I can't imagine how economy passengers are treated.