Can not call other Comcast users on landline

I have the Netgearc7100v approved comcast xfinity modem. Everything was working find for many months, but since 7/1/20, when I call another comcast member, I can hear them but they can not hear me. Only happens with other Comcast subscribers. All incomings calls work without issues. I can place other outgoing calls without issues. Called Comcast customer service and they could not figure it out. I have reset the modem, reset a signal without the problem resolving. Please advise.