Unable to browse internet after usb modem disconnects and reconnect

Greetings,

I have done a fresh install Ubuntu 16.04. Usb modem works fine after boot up, but if modem is disconnected, I have to restart in order to get to browse the net again. If I just re-connect the mobile network, the icon in the task bar shows that the pc is connected to the internet, but the browsers say that thereare no internet connection.

I have searched the net for few days now to no avail.

I need help with this please!

Thanks