I fully support the fact that your raising the error helped the other students and you deserve to get bonus points for that. One may argue that other students might have wasted time on that too, and if they did, then in their answer sheets it will be reflected in the order of answers they attempted and they might get some points too.
In any case, you deserve a few points, maybe not 19/20 because one could argue that your test-taking strategy is flawed.
Another alternative is you get a new test with 16 as minimum points irrespective of your new score. This would require the teacher to set another paper, which they must do as they failed to set a correct question paper in the first try. Any other student who attempted the same question earlier than other questions must be also given the chance to write the exam.
In my opinion, you are well within your rights to take this up, especially since the teacher did not hear you out. It was their mistake and you must take it up with the dean in your university. Or maybe even someone higher up the rank.
I had a somewhat similar situation in high school. Suddenly there was a ceiling imposed on the marks awarded in tests, after the evaluation. Except for mathematics, no other test can have more than 80% awarded to students. I was the only student in the class to get more than that in civics and science. Instead of scaling it down proportionally for all students, the teachers conveniently just cut off my marks. I successfully raised it with the school principal and got the exception. The fact that I succeeded in getting that done was more helpful to me in my life than those exam results. I faced the ire of the teachers when I argued with them and then went to the principal. Your case is of course different, but there are some similarities too.
You standing up for what is right and not giving up is a more important test than the one for whose points you are contesting. So do not give up.
I would also like to add that a large number of answers on this platform are from academicians who tend to give answers which put their fellow academicians in a safe place, probably not even intentionally. So read every answer after considering the fact that the person answering it might not be neutral. After all, the teacher is at the wrong end in this case and he has no right to push you over.