Thanks very much for your advice.
We finally found him by going down to his workplace. He said he had to clear debt and paid upfront for a 1 year rental. Therefore he wanted to withdraw because his remaining sales proceeds from his flat is insufficient to pay for our flat.
We were appalled because he just got his sales proceed a week before completion date!
He agreed to compensate us for withdrawal at the 11th hour but didn't reply us again when the agreed date comes. We are consulting lawyers today and would proceed to sue him if he still doesn't appear to compensate us for our loss, We have to frantically look for additional bank loan and cash without our sales proceed to pay for the resale flat that we already completed first appointment. There's still additional property tax, electricity and conservancy charges because it will be impossible for us to sell our flat in such a short time.
Fortunately, HDB allows us to submit appeal for timeline extension request to sell this flat if we can't sell it within 6 months after completion date of our purchased flat.
