A shadchan needs to be paid
The Steipler frequently asked people who were experiencing shalom bauis problems or fertility problems if the shadchan was paid. Get the source and send a shaliach to them to explain why this is a bizayon, why it can have negative ramifications and why al pi Shulcha Aruch of law and of midos they need to fulfill their chiyuv.. The florist got paid as did the caterer, music, hall, landlord etc. now the shadchan. When I am mesader kiddushin I inform them that I will not get under that chupah unless the shadchan is paid.
No chiyuv to be mochail a monetary obligation without due reason and cause.
Hatzlacha!