I had a similar problem with a 30-day card. I was reluctant to send it in for a partial credit because it was shortly after the fare increase and my replacement cost for the remaining weeks was going to be greater than my original cost, and I think I had a week-long vacation coming up, too, which further messed up a potential replacement, so I ended up swiping repeatedly at various turnstiles (after a day or two, I knew which ones would work for me). But the day none of the turnstiles at my home station worked even after repeated swiping, I gave up and sent the thing in. I did receive a letter and a partial credit quite some time later.
I can't wait for Oyster-like cards!