Bluetooth Volume Low on Calls in Car

Since a recent upgrade, volume is low when I make a call using Bluetooth through my car stereo. It is ONLY when making calls, not any other Bluetooth activity (like maps, etc.).

And please don't suggest "adjust the volume while on Bluetooth." I have done that and even with the BT volume (and stereo volume) maxed out, you can barely hear the other person. The other person can hear me fine, though. I am using the most up to date OS (12.1.2).

Also, speaker phone works fine. It is ONLY BT calling through the car stereo.