Cooling off period

I had a new tenant who posted the keys to the property that he had taken over 2 weeks earlier through my letter box saying that he had decided that he couldn't afford the property and so was exercising his rights to a 14 day cooling off period.

I replied that it would have been common courtesy to call me to discuss the situation 1st and that the cooling off period was 7 days so the contract remained until I could find a replacement tenant.

He then responded with a tirade of abuse about the property (all completely untrue and unfounded and is in excellent condition). Demanding his money back or he will see me in court. I have told him that I will do my best to find a replacement tenant and will refund him part of the rent he has already paid (if) I find a new tenant less my costs in finding the said tenant.

What are your thoughts on the subject? All good advise is apreciated.