Thanks for posting and welcome to the Bose Community. I am deeply sorry to hear that you are having some issues when making calls on the QuietComfort 30's and would love to assist you further.
Firstly, I would recommend that you ensure that the headphones are running the latest software version by connecting them to a PC and using our Bose Online Updater here, the latest software version for these headphones is currently version 3.0.3 as of the 7th of November 2019. I would also like for you to test the headphones with another device and calling software such as Skype or Whats-App to see if the same call audio continues.
Please can you also perform a standard product reset on the headphones by:
Power off your product, then wait 30 seconds
Connect your product to a wall outlet using a USB charger, then wait five seconds
Disconnect the USB cable from the headset, then wait one minute
Power on your product.
Can you please also confirm if the answer/end call button works correctly with the headphones? If you are unsure which button this is, it is the multifunction button that is located in the middle of the in-line controls on the headphones.
I look forward to hearing back from you with the results of the troubleshooting steps above. If any other users in the community are also experiencing this issue please do let us know in this thread below.