Replying an official letter

hi

i am working in a petrol station and there is this client who is requsting fuel on credit basis, he is therefore asking our terms and conditions applicable to those client that takes fuel on credit.

and since those client pays their fuel on monthly basis after we submit our statement at the end of the month and we give ten days upon reciept of the statement for them to clear their bill.

i am therefore requesting you to help me on how i could put this on a offical letter and what will be the letter heading?

please help.

am maro doyo.