I WRITE with reference to the letter headlined, ''Extra buses for 641'' (South China Morning Post, July 21). My records reveal that the Transport Complaints Unit has not received any complaints against Cross Harbour Express route No 641 from your reader Mr Albert Leung. The unit, however, did receive two complaints of a similar nature from another member of thepublic, and the Transport Department is arranging a survey to assess the demand situation and level of service of the route. I wish to reiterate that members of the public can complain direct by telephone to the Transport Complaints Unit. the unit's hotline (577 6866) operates 24 hours a day throughout the year. Alternatively, they may write to us at ''P.O. Box No. 30789, Causeway Bay Post Office, Hongkong''. S. W. CHOY for Executive Secretary Transport Complaints Unit