A GENERAL manager duped his plastics company out of more than $7 million by pretending that customers were ordering goods - and then using their credit to buy up the merchandise himself. In 1993, Yuen Chap-fai, 32, held the top position at Muelstein East Asia Limited's sales department. In August of that year credit manager Lam Ming-kong discovered that 18 customers had not paid their bills. But when he telephoned them to ask why, he found that none of them had ordered the goods listed on the invoices. Yuen's accomplice, assistant sales manager Chan Kan, 36, had arranged for $7.2 million worth of merchandise to be released from the warehouse and sent to China through an intermediary company owned by Yuen. The general manager's private company would never have been allowed such a long line of credit if they had not used the bogus orders, the District Court heard. Yuen and Chan then doctored Muelstein East Asia accounting documents to cover the trail of deception, prosecutor Phillip Ross said. Yuen and Chan, who denied the charges, were both convicted of false accounting. Chan was yesterday sent to prison for three years, Yuen for 31/2 years. Deputy Judge Andree-Wiltens cited Yuen's senior position in the company as the reason for the variation in the sentences.