You are entitled to a full refund when a train is canceled. What you decide to do after that is up to you. You will be charged the lowest current fare on the train you decide to ride on if you go to the ticket window.

What I have done and what YOU should have done instead is to keep your old ticket and board the next train to your destination in the same class of service (i.e., don't board an Acela if your ticket was on a Regional). When the conductor stops by tell him your train had been canceled and you are boarding the next available train. There's a 99% chance he will take your ticket on the comparable train and a 1% chance you will be put off at the next stop.

Once on a very cold day, I was waiting on the BWI platform and did not board the train that had just stopped because I had a ticket on the next train. The conductor walked toward me and asked where I was going and I told him WAS. He said, go ahead and get on, which I did on the Acela - my ticket was on a Regional train. The conductor felt sorry for me because it was so cold outside. ^

My best friend is an Amtrak conductor and they have very wide latitude when it come to accommodating passengers!