I have problems when sending audio to a Bluetooth device or headphones. Basically there is no volume to Bluetooth and only very low volume to a lightning-connected device such as headphones. In addition, when I adjust the volume using the Bluetooth device's volume control, my phone indicates that volume is at 100% or 0% - no in-between. However, audio sent to a car's audio system, either via Bluetooth or a lightning-to-USB cable, works just fine. This holds true across many devices - I have access to lots of headsets and Bluetooth speakers, and I frequently rent cars. Any thoughts? The nice people at the AT&T store say I have no choice but to buy a new phone (surprise!), but I'd like to see if I can fix the problem first. Thanks!