Dear Mr. Yang,
Based on your agreement with XXXX you have to give a 6 month notice to be able to terminate your employment with the company. We do not agree with this notice and to the best of our knowledge no company in Singapore is allow to employ you while your current employment agreement is in force. Please be advised that you are liable to the damages that you are causing to XXXX and its customer. XXXX will reserve its legal rights regarding your breach of agreement.