Someone elses Spotify on my mobile phone

[Neesuperdoei]

Hi! When I am at work and online via the Wi-Fi of the building my phone (HTC M9) regularly gives a notification that Spotify is streaming via Google Cast. The weird thing is that I don't have Spotify on my phone or even use my Spotify account at all. How is this possible? And more importantly: how can I prevent this?

I've secured my phone with a password and Kaspersky security app. It only happens when I'm in the office. The building hosts many companies who all use the same network so my employer can't do anything. I hope someone can help me out. Thanks in advance!