No, it is not possible to get a refund for unused days. 

I’m not using my global Eurail pass as I cannot get any seats from Paris to Amsterdam due to the  rrail strike issue

There are also other options available, e.g. Eurostar to Brussels and continue with reservation-free trains. Or TGV to Lille and then reservation-free trains via Antwerp. On what date and time would you like to travel? Do you have a 1st class or 2nd class pass?

Eurostar availability is always limited if you want to travel on short notice.