Find out who the lawyer was who was acting for the estate. If it's not readily available for you, you can get a copy of the probate file from the Supreme Court, and the solicitor's details will be there.
The cheque may be stale, and might still be unpresented from the solicitor's trust account (best possibility).
Or the solicitor may be able to tell you when the cheque was banked, in which case someone else took your money.