人不在香港，匯豐銀行的帳戶不想再用了，如何取消？

you can give them a clear written instruction
clearly stated your request and situation, plus how would you like them to handle the existing funds in your account, and if telegraphic transfer is needed, then where you wanna debit the service fee from.
if your account is an integrated account, the account will keep on charging you the below balance fee, so don't wait till it auto close, coz then you will be chase on your debt - the accumulated below balance fee.
so, inform them in a formal manner to protect yourself.