Ong had on May 20 paid nearly 22 cents each for 5.55 million shares.
Ong's actions came after a group of investors on May 15 launched a takeover offer for the company at 20 cents each.
This group of investors include a subsidiary of Cosmosteel's single largest shareholder Hanwa Co, a Tokyo-listed trader of steel and other materials which now owns 31.61% of Cosmosteel.
Cosmosteel closed at 22 cents on May 22, down 4.35%.
