I was in the same boat a couple of years ago with some older tickets. I do believe most of the parks have a customer service area close to where they sell the tickets. They can tell you there if you have any days left on your tickets (and how many days.) They can also reissue the tickets there for you as well.

If you are staying at an onsite hotel, some of them at least will have a concierge where you can buy park tickets. They also, were able to help me by scanning my tickets and telling me how many days were left.

I don't remember being able to call in and them tell me how many days were left on the tickets, though maybe things have changed or maybe I just didn't talk with the correct customer services. But I had to actually go to WDW to get them to scan my tickets and re-issue them for me.