Hi max,
I did more or less the same thing a few years ago. We had the house on the market with an agent but ended up selling the house to a friend of a friend. After we had received the deposit, I contacted the EA and said we had sold it ourselves and acted dumb and said, I assume we dont; owe any fees and they agreed and we were never charged.
I would have expected to have got a bill for the advertising, signage etc but never did.