Handsfree calling in my car doesn't work after successfully paired to my new iphone 12, worked fine on my iphone 6

No, as I wrote already the pairing goes perfect. I’ve paired Bluetooth phones to a lot of cars that I’ve owned. I’ve been doing it well over 10yrs. I enable pairing on the phone then tell the car to pair. It gives me a 4 digit code that I put in the phone to connect to the car’s Bluetooth and it’s done. Same as my old iPhone 6.

The proof is whenever I start the car it finds my iPhone 12 and reports it’s connected to Bluetooth on the dash. My phone reports it’s connected to the car in its Bluetooth settings.

Perfect! Except it doesn’t work.

When I make a hands free call the car says it’s making a call using my iPhone 12 then a box appears on the phone offering speaker choices including my car which is the one already checked off automatically.

However no rings are heard on the car system and if someone answers they’re not heard.

Sometimes the phone switches back to its own speaker, or sometimes I have to do it manually, often while driving of course. Tons of fun!

Sometimes when it’s still showing my car selected in the box I can hear the phone speaker ringing faintly as though I was holding it to my ear. Of course it’s supposed to be silent while using the car’s system when that’s the selected option.

Switching the phone choices during an active call back and forth from iPhone to speaker to car doesn’t help either.

When I get a call in the car the same fail occurs. I haven’t tested if anyone can hear me talking in the car on the other phone. At this point it hardly matters.

So the car It won’t work with is a 2010. I have 2 other newer Bluetooth cars that also worked just fine with my iPhone 6 when I left them up north last December. But I can’t try them with the new phone until next month when I migrate north for the summer.

And of course I’ve unpaired everything and re-paired it. And I’ve rebooted the phone. Makes no difference.

Comments welcome.