All you have is speculation due to coincidence. How do you know that the owner did not sell lit to his friends/relatives? If so, they can say that they never saw the house while it's listed with you, then how do you prove it?
In CA, in order to claim a commission after the contract expired/cancelled/withdrawn; we have to provide seller with names of people who were shown during the listing period, otherwise, we will not be entitled of commission.
Terminology is important. This is not legal advice. Consult an attorney if you need advice.
1. Talk with your broker.
2. If the listing is withdrawn, that means there is a legal relationship between the owner and you.
3. Did you provide the seller with a list or agents and/or buyers whom had contacted you about the property?
4. If you can prove that the seller had contact with the buyer during the listing period...that even means a phone call or visitng the property, then you may have a case.
5. Either way , discuss with your broker.
I very much agree with Vicky, check with your broker, that's what they are there fo, they have to carry the torch on this, and that is why you need a good one. I also agree with Vicky that it is hard to imagine a pretty outcome. Sorry the seller did that.