Do not use Dormehl as they might try to cheat you

I appointed Andy Wade of Dormehl Property Group to market my property. I was not happy with his service so cancelled my agreement with them and marketed my property privately. I received a list of potential buys from them so that that i did not accept an offer from somebody they introduced the house to. Today 4 months after accepting an offer I receive an email form Christo of Dormehl confirming that Andy introduced the client, and gave me an offer that i did not accept so they want the commission. Not only was i not given an offer from Andy but my buyer does not appear on the list they sent to me.