Connecting to random BMWs

[rjneid]

Hi, 

I recently was travelling and connected my iPhone's Spotify to the rental BMW's Bluetooth. Now that I am home, whenever I'm driving my BMW and a different BMW is nearby, my Spotify will automatically connect with the other car. My music will stop abruptly. This happens also with my desktop Spotify where there are no cars around. 

Please tell me how to fix this. I don't seem to be able to find a setting to disconnect from BMW's in general.