British Airways - cheated and mistreated by british airways

This complaint is regarding a flight booking we had with British Airways.
Before we made the flight booking we had called British Airways to see if everything would be ok to fly with BA through London, and they said everything would be fine. Apparently this was just to get our booking confirmation. Our initial flight was on **-**-**. We arrived at the airport well on time, the ground staff checked our documents, but first told us that we needed an online BA registration for our * year old daughter as well. This was never communicated by BA, we only got * link per booking, but we did this at the airport, and showed it to the ground staff. All the while, I kept asking if there was anything else that we should do and/or check already, but there was no need according to them. Then, when finally our daughter's BA application was approved by the UK team, they told us that there was a PLF form needed as well, for the transit in the UK. We were unaware of this, as it was not communicated in the mails by BA to us, and the Team Leader at that time was extremely rude, told us it was too bad, closed the check-in counter and said we would not be able to board.
Completely flabbergasted we stood there, ready to go home to our house in India, but treated like scum by the BA staff. I repeatedly asked if there was anything else we could do, or keep in mind for the next time, but she kept on saying that it was our own fault, and everything else was ok, but we needed a PLF form. I have never been treated this rudely by the staff of any airline in my life.
I then spoke to the phone number of BA that I got from another counter. They rescheduled our flights, but we could not fly until Tuesday *-**-**.
So we had to make arrangements to stay in The Netherlands in the meantime, repeat the Covid tests, rent a car again etc etc.
On the *nd, we again arrived at the check-in counter early. We had uploaded everything into the BA site, the Indian government site, etc. The lady behind the counter checked all the documents, checked me in personally, as I was on a different PNR, and then tried to check-in my wife and daughter. First she couldnt find my wife's documents on the BA site, even though I had a confirmation of that the day before already. After a long time and internal calls she finally found the details, and mentioned that EVERTYHING was ok, except for the PCR test of our daughter, this was not communicated during the first time, at that time they said that everything was ok, besides the PLF, but now all of a sudden they insisted on a PCR test for our * year old daughter, even though it clearly mentions on the Air Suvidha website that kids under the age of * do not need a Vaccination report or PCR Test!! Even though I found it terrible to put our daughter through this, I did not have time to argue with the BA staff, so, I took our daughter for the PCR test and paid