If the broker did his part like he got you a flat which you like then donโt you think he deserves some Compensation in return. He spent his time, money and used his connections to find a flat that you might like so he deserves his share if this deal goes through.
No one should work for free. Even fuel is around โน100/liter now. He must have shown you multiple flats before finalising this I guess. I guess thatโs why he threatening you but thatโs wrong.
Talk to him and find a common ground I believe.
He might agree with 60-70% of his fees