[austin]

Hello Armando,
As far as I know, you have no obligation towards the estate agent. The only thing is, you will have to contact someone and ask them to return the key - you can explain that you are now selling your house privately - presumably you have nothing in writing from them from what you say? Do you even know if they have your key, did they acknowledge it? You don't have to speak to the same person, anyone in their office would do. Failing that, you could send them a registered letter in which you state you are making a private sale and asking for your key.
It is very usual for them NOT to return phone calls, I had this happen to me numerous times, when we were actually cash buyers and yet they did not seem to be interested at all, could not have care less, so much that you wondered whether they were in business at all!!! I'm sure you are better off selling to a friend: no agent?s fees for anyone for a start! But you will still have to go through a notaire here in France...
Many Thanks