@wouthermans: Please try typing in the IP address of your Pi (should be displayed in your router’s web interface) in the URL bar instead. Then try renaming your device in Settings/Reboot.
@gerstel: Usually the router should recognize the confusion and assign the new Pi with a new IP address. Have you since rebooted the Pi or observed any changes? Is it in fact possible that there is a conflict, however this is usually resolved by the router which assigns a new IP address to the new device.