Unfortunately, if you did legitimately owe him money, there was no "false pretenses"--you owed him money; you gave him a check; he cashed it. There is a common misconception that the memo field of a check has some legal effect and can control what the check is used for. That's not the case; the memo field is the equivalent of a "post-it" note--it can jog the memory as to what a check was for and help with bookkeeping, but is not legally binding. Note that if  you owed him money, the contractor coud have sued you for what you owed him, so you're not behind if he simply cashed the check. If you did not owe him money, or did not owe him that much, that would be a different story, however, and you might have a cause of action; in that event, you should consult with an attorney.