Dave,

On the assumption all the above is correct and you have copies, sent recorded etc. you should just send them a letter saying that unless first installment chq is received within 7 days and your claim is fully reinstated you will issue a Court summons using the small claims proceedure via  the online moneyclaim website. Do not elaborate or waffle in the letter.Tell them that no further correspondence will be entered into other than to acknowledge receipt of chq etc.Obviously send it recorded. If they don't pay then DO IT via the moneyclaim site. Trading standards will just tell u the same. This is the only way you will get any money.

Neill