This was not a parcel, but a letter. It is unusual to use a delivery confirmation on a letter, it is generally cheaper to just send it Certified. I saw a DC on a letter today, though, and it is the only one I can remember seeing. (I'm a letter carrier too.)
I would think that if you have the DC number, there should be no question about following it up. Did you put the DC on the letter, or see the clerk put it on?
You would no doubt, in any case, have kept the receipt for the transaction and can prove your claim using that. It may require a trip in to the Post Office where you made the transaction. I love my job, hate the Post Office, and will not ship with any other carrier, given a choice. The USPS has shown me the best service with the fewest losses/breakages.
Killdeer