However, my non-legal supposition is that if the two of you owned the house at the time the listing contract was signed, then both of you should have been signatories to the contract. If you weren't, then that contract may be invalid. If that's the case, it doesn't suddenly become valid just because the divorce is finalized or even that you subsequently signed a quit claim deed. Was it valid when it was signed? That's questionable.
Still, as a practical matter, since you signed the quit claim deed, you have no further interest in the property.
Finally, one thing that may have occurred is that your ex husband may have signed a new contract with the agent following your divorce and the signing of the quit claim deed. If he was the sole owner of the property, he'd be able to do that.
Check with a lawyer for more information.
NMLS # 6395
Financing Kentucky One Home at a Time