Concept:A credit note is a commercial document used by a seller to reduce the amount a buyer owes when there has been an overcharge or adjustment.
Explanation:When a buyer is overcharged for goods supplied, the seller must correct the invoice amount.
The seller issues a credit note to inform the buyer that a credit has been given for the excess amount charged.
A debit note would increase the amount payable, not reduce it.
A proforma invoice is only a quotation before the actual sale.
A letter of credit is a bank guarantee for payment, not a correction document.
Therefore, the correct instrument for this situation is the credit note.
Answer:D. credit note