From: Rabbi Moshe Sofer
To: Rabbi Ber
A husband who sent a get via an agent then dispatched a second agent to delay its delivery, but the second agent had no written proof and the first agent refused to accept his verbal claim and delivered the get. The Chasam Sofer rules the get is valid on multiple grounds: cancellation via a second agent without two witnesses fails by the Yerushalmi's standard, and under the Rambam and Shulchan Aruch the first agent was not obligated to believe the unverified second agent. The husband's words to friends expressing a desire to delay also did not constitute a formal bitul, and the ruling is conditioned on agreement of two additional qualified scholars given the severity of the matter.
Source: Shu"t Chasam Sofer EH II §50