I think the biggest issue here is that you didn't read the room. Ideally, sure. You don't jump to giving numbers out. Your pre-prepared answers were OK. But based on your description, there was a point where the HR person was making it clear to you that they were looking for actual numbers from you. In my opinion, this would have been the time to pivot, and throw out some numbers on what your salary expectations were. I'd have said something along the lines of "Based on market rates for this position, and factoring in my current salary, I would need a salary of X in order to justify leaving my current position." Something along those lines. Instead, you stuck to the generic advice of not giving any ground. This particular employer called that bluff.