I have valid L1B visa but could not travel due to personal reasons. Can I still get the Visa extended?

I have a valid L1B visa from Sept 2015 to July 2018 (PED) and expiration Sep 2018 but I was not able to travel to US for work due to some personal reasons.

Can I get my Visa extended even if I do not travel once to US?

When can this be done and what would be the procedure for it?

Also what would be the duration of extension? Can these 3 years be recaptured against unused time?

Thanks in advance for all the help!