Why do calls to this device get picked up by other devices?

1. Go to the phone menu and select settings, select Calling Accounts and then “SIM settings”
2. In this screen scroll down and select “Call Forwarding”
3. Check if the “Always forward” option is enabled, if this is the case disable. In this screen there are three further options “forward when busy”, “Forward when unanswered” and “Forward when unreachable”
4. Enable/Disable the functionality you desire