Booking.com complaint: ‘We Price Match’ doesn’t match

Booking.com offers to give back price difference, if you find the same accomodation at a lower price on another site. I called them and an operator checked websites with me (we checked both offers in $$), ed that they will pay be the difference back and asked me to book the apartment and send them the screenshots.
I followed their instruction – booked an apartement in $$ and sent them a screenshot from another website in the same currenc ($$)y for the same conditions.
After that they declined my requirement, because the currency of the host differs. That was never written in the rules and they couldn’t show me the line they’re reffering to – the unswer was just Tahts’ it, we can’t prove it, just believe. In the end of the very tense conversation the manager hung up the phone without saying goodbye. Very rood. I’v very disappointed.