For mobile there is an option to prevent it but I would like to block the updates and background data on Wifi also because I am connected to a Hotspot that uses Mobile Data from another mobile phone.
You can define that hotspot as being a "mobile hotspot", so Android would deal with it as if it were using mobile data:
- Open Settings
- Go to Data Usage
- Tap the "overflow menu" (the 3 dots in the upper right)
- From the menu opening, select Mobile Hotspots
- Put a check-mark next to the hotspot you're using.