British Airways complaint: I’m stranded in Delhi

I arrived for my delayed BA 256 flight from Delhi to London Heathrow LHR. I had all the documentation required but was told that I couldn’t check in because my Negative PCR Test, signed by Himachal Pradesh’s chief medical officer, wasn’t valid because it didn’t have a QR code. I called the Government Hospital where the test was done and they assured the British Airways associate that no Hospital in the state of HP are issuing QR codes and it was obviously valid because hundreds of people had flown with them already. The associate refused to let me check in, I missed my flight, and was told that I wouldn’t be getting a replacement flight either.
In the meantime, two of my friends from Himachal Pradesh with the same PCR certificate boarded their flight to Switzerland and are now headed for Europe.
After the flight closed another BA associate said it was a shame that he hadn’t been there to check my documents because he would have been able to help me properly.