Hi Lori,
i just had the same problem as you with Australia's Telecom provider, with a missing $430. The cheque was always in the mail when I inquired, I still haven't received it!!! In the end I insisted on speaking to a manager in credit control after about 6 months of wrangling. They say they can't transfer the money to your account, but they can, so insist it comes back to you as a credit on your bill, don't trust them to send a cheque.
I'm probably stating the obvious here, but I suppose you have already tried the phone book to find your lady?
Cheers,
Jill