In my experience their response can change quite quickly if you quote the relevant articles of the regulation and if you can find one, a court case about a situation very similar to yours which was ruled in favour of the passenger.
They once tried to get rid of me by saying that my connecting flight had left on time, but I had been a no show. The fact that I was stuck aboard another one of their aircaft which had been delayed (no force majeure) was irrelevant to them. The second flight had left on time but I had missed it
.