There is no such thing as a "verbal promise" when it comes to business. The fact the estate agent did not want to give you anything in writing, should have rung warning bells in your mind of what he had in mind. In your situation, there is nothing much you can do. What has taken place with you is common here. The fact that he is holding your cheques gives him a leverage. The estate agent knows all this. There is no benefit for you in going to the court of law. It usually takes several months for the court to give its verdict. Just swallow this bitter pill as a bad experience in life here, and bear it out.
If you ever have a choice as Brit has said, shoot the estate agent twice and then also kick him hard even if he is dead to take all out all your frustrations.