Respected Sir/ Madam,
This email is in reference to the payment of credit card _______ (card number) in receipt of ___________ (mention).
It is to inform you that we have received the payment of amount __________ (mention amount) for the credit card repayment for _____________ (mention duration/ quarter/ any other) and we are thankful for the timely repayment.
[Digital Signature – if applicable]
____________ (Contact details)