check still shows cashed on their end
What answers do they give to Where's My Money questions like:
-What account was it deposited in - what bank, what account number, etc?
-What is the time, transaction number, and other identification information of the transaction?
-Can they provide an electronic or physical receipt from the recipient bank acknowledging the above?
Anyway, since you got a flicker of assistance already, here's hoping you succeed soon.