I have an EA friend who has tried to obtain his fee's more or less in similar circumstances to the OP but has never won his case yet.
Susiecam more less has it right in as much you have to have a signed contract for 'sole agency' or 'sole selling rights' and as you have,according to you, not signed anything then you are just not liable but you don't need to take my word for it or anyone elses go and get it confirmed from a Property Lawyer who for a small sum will write a letter on your behalf to the EA concerned.
Mel.

PS Back to work Susie...you have work to be done!!

I would say you definitely need a solicitor's advice in this regard, though not if the conveyancing solicitor was recommended by, or has any relationship with the EA.

Many years ago, I side stepped my selling EA. I had a knock on the door from a potential purchaser who had been trying to fix an appointment but frustrated at the EA's total incompetence, tracked down the property from the photo himself and simply banged on the door. We did a deal, and I simply told the EA I was taking it off the market. They were so inept, not a single question was asked.

I would not recommend this course of action, however!!