If you cannot say “No” then say “Lo”.
Also, try & call the Shadchan at a time when you believe s/he shall be out and you are likeliest to get an answering machine, and then just be firm & decline, and explain that it is not your normal policy nor mode to decline, and ordinarily you give the potential candidate at least a 2nd chance, but in the given situation you simply don’t want to give any false illusion.
Of-course if the Shadchan has an e-mail, and the Shadchan won’t take No or “Lo” over the phone for a response, just send an e-mail [irrespective of what anyone at the Asifah ever said]. Makes sure your message or e-mail is in English & not in Yiddish.
Of-course also:- Always thank Shadchan profusely for his/her time & efforts, even if you don’t mean it. ………. & if Friday or Rosh Chodesh or Ellul, add Good Shabbos/Good Chodesh/Shono Tovo in your message, even if you are irate at the Shadchan.