Should I pay a penalty?

I am writing you to ask the question about the situation I had got into regarding house rent. I was searching a house because recently I moved to the Netherlands. I found one and had an appointment there. My estate agent secured it and I wrote him a mail (“Ok, let’s proceed with a contract”) and landlord started making a contract. He did it for a long time and during this period I decided to rent another one apartment, so after receiving contract from the landlord I told him that I’m not interested in this property anymore. Now he is asking me for one month penalty and already provided me an invoice because he thinks that we have entered the legally binding agreement despite the contract was not signed. I am not sure that I obliged to pay it and don’t know what consequences it may have. Also the amount is quite high for me, it’s 1800 Euro. Could you please provide your legal opinion in a few words?