If a Customer is getting sounds from their call through their speakerphone and headset at the same time, there is possibly a way to remove the sound that is coming through the speaker phone.
First, if it’s possible to do so, change the phone over to speakerphone mode
Next, adjust the volume on the phone all the way down (when in speakerphone mode, the volume control will only control the level of the speakerphone)
Finally, change back to headset mode in the phone.
Boom! Sound should now be coming from the headset only and not the speakerphone :)