The first letter should identify the proceedings, reference number, counterparty and your role. Attach an evidence matrix listing document, date, amount, entry, purpose and its significance for allocation. State whether you seek separation, a reconciliation, repayment or, as a precaution, filing of a claim.
Request confirmation of the balance, transaction records and treatment of the money. Do not assume that a deadline in your letter is a statutory deadline. Procedural time limits and the proper form of assertion must be checked against the court notice and the specific proceedings.
Avoid setting off against, accessing or blocking an account yourself. Those steps can create further legal issues. A complete, factual and provable presentation provides the better basis for the next decision.