I can’t make phone calls and my phone won’t connect to my car

That this is both cellular calls and access to Bluetooth implies a fairly low-level hardware problem, if not something such as Airplane mode having been enabled. And that doesn’t usually block Bluetooth.

If there are any add-on VPN clients, remove them and test again.

Then see the following link > If you can't make or receive calls on your iPhone - Apple Support

Which includes restarting the iPhone. Restart your iPhone - Apple Support and resetting network settings Return iPhone settings to their defaults - Apple Support

Then use the Get Support link in the upper right, and discuss your options and alternatives with Apple. I’d tend to guess that the communications hardware of this iPhone 6s just gave out, though. And that hardware is getting pretty old to repair.

Okay, so this is two now-unrelated questions...

You’ll want to check for the documented features and limits of your particular vehicle entertainment system, look for and apply any available firmware updates for your vehicle entertainment system, and then check with your vehicle dealer.

Most (all?) vehicles with entertainment systems have had firmware updates in recent years.