Since billing errors tend to snowball with interest charges, etc., it's important to put the details down in writing and urge a quick resolution to the problem. Enclose any supporting detail you have as to why you believe the charges are incorrect.
1234, Main Street
Boston, MA 02123
<Recipient Address Goes Here>
I would like to dispute your recent invoice, invoice number <invoice number> for <$amount of invoice>. I take exception with this amount because <reason for disagreement>.
I will be happy to remit payment when I receive an accurate invoice. In order to clear this up as soon as possible, I would appreciate your prompt attention to this matter. Thank you.
encl: <List of enclosed items goes here>