Drafting a Particulars of Claim

A company in London Essex designed and supplied a kitchen which was significantly different from described and flaw in the design meant a dispute had to be raised.It was disheartening but convinced myself to go along . The company verbally agreed to refund money for the some units returned and also for those not delivered but has been avoiding it. Filed and online claim for a amount £568 Plus the court fees. Now need to send them a detailed Particulars of my claim