Can you force your opponent "off line" ?

I was playing an end game and was one move away from winning (and actually made such pre move) with still over 3 minutes on the clock, when all of a sudden I am "off line".  This is not the first time it has happened. How can a computer hack chess player interfere with my internet connection,  when I am listening to you tube music at the same time on the same internet connection.  

If you have 3 minutes on the clock and one move away from mate, refresh the board. This keeps you connected in some way. If my opponent stalls I also experience the same thing. So, just keep refreshing every 10 to 30 seconds to make sure you are connected to the server.

Thanks, but how do I refresh the board ?

Refresh the browser.

Press the F5 key. On some browsers it's <control>-R instead.

thanks, I will try your advice next time, as is apparent I am not a computer fundi