Any lawyers out there who can ansewer?

I had a check from a doctor who I over paid. The check was for $425. I lost the check and forgot about it. When I came across it a few months ago I didn't see an kind of expiration on it, but I called the bank that it was issued from to see if I could still cash it. They said that they wouldn't accept it after 90 days and that I needed to ask them for a new check. I have been calling the office manage (supposedly the only person that can help me) every day now for 2 months and she won't return my calls. I have a friend who is studying law and they told me "A check is a legal claim against funds, period. Meaning, an "expired" check does not deter from the fact that someone owed you that money at one point in time, and there is no "expiration" on that intent or obligations of funds to you. Even if an expiration is there, it has no legal standing." Is this true? What are the legalities to this? Am I just out of luck because I waited too long or is there something that I can do about this?