I am using an iPhone 6, and what I do is go to "Settings" on my iPhone, tap "Cellular", and then under "Use Cellular Data for", turn it off for "Spotify". That helps to prevent the Spotify app on my iPhone from connecting to my laptop when I am using Spotify on my laptop. Of course, it goes without saying that if you want to play Spotify on your iPhone later again, you need to enable Cellular data for Spotify on your iPhone later. It is a bit tedious, but it is the simplest solution I have so far. For other phone users, I suppose you can use the same concept to essentially choose to disable the use of Cellular Data for your phone when playing music from Spotify on other devices.
A while ago I was connecting to random devices that I don't know and I emailed Spotify and they told me to disconnect the device and change the password. I did and just recently I keep connecting to another unknown device playing different music. LET US TURN THIS CRAP OFF. I'm going to subscribe to Google music or something. You guys can't take the hint that maybe you have a serious problem.
This needs to be fixed ASAP. If spotify thinks this is an acceptable way to deal with customer complaints then they are hugely mistaken. I'd want to know who is, most likely, getting paid lots of money to drive your customer feedback and user experience teams; because they need firing immediately.