As we can see I have expanded stations like the police stations and ambulance stations. My police station cost me 481k but I expanded it 6 times... On the ambulance station when I expand a small ambulance 6 times for 360k and another 100 for the station it gives me back all 460k. The same goes for a fire station I spent 25 coins on and 360k upgrading the slots but did not receive any of that money back. I can conclude, expanding slots for fire and police stations will not give me back the money I spent on expanding them.
This was not the case before I 100% know it. I believe it is a bug or the devs really wanted to nerf the system. It cost me quite the hefty fine for this. Even if this was something the devs nerfed I don't think it should have been this discrete.