Carplay won't play phone call audio through car speakers

My aftermarket JVC-Kenwood car audio system used to work perfectly with Carplay in iOS versions less than 13. Since iOS 13, I am facing a weird issue.

Carplay (wired) is connected and set up correctly. Spotify and Maps work perfectly (with audio directions).

When I make a call using the head unit, the ring tone plays through the car speakers, but when the called person respond, the voice audio comes from the phone speaker and not the car speakers (barely audible).

I am now on iOS 15.1.x, same problem persists.

I have Accessibility -> Touch -> Call Audio Routing set to Automatic.

I found some posts on the web (Reddit), where users mentioned that this is because starting at some iOS version, voice audio is not routed through all 4 car speakers. I took the car to the service center (where they had installed the car audio system some years ago), and they found no issues with the connections.

The only uses I have on Carplay are Maps (Google Maps, mostly) and Phone, and they must switch seamlessly from the music that is playing on the USB (or Spotify) and work together.

Any help would be tremendously useful.

Thanks

AB