Bluetooth doesn’t make much sense, as you usually only have one device active. But you can easily rule this out: If you have Android for example, long press the Bluetooth button, then check paired devices. Is there any device you don’t recognize? Remove it. Done.
Bluetooth is usually encrypted, so if you didn’t accidentally pair your device with your neighbor’s there is no way they can listen in.
And even more important: Check for carbon monoxide in your home. You might be having health issues and are hallucinating or making things up.
Besides that: It might be possible your neighbor hears you talking on the phone (through the walls for example or with a bug in your home), but there is absolutely no way they’d hear the other side of the conversation. So either your side alone would already give them all the information or something else is up (see above).