Client made overpayment

Client made overpayment of $800 on account.  I initially applied a credit to the account.  The client stated that this created a financial hardship for the family.  I then wrote a refund check for the $800 out of my business account.  The clients billing continues to reflect the $800 dollar credit.  As a result the payments due for 04.25.23 & 05.09.23 for $150 each were simply deducted from the credit.  In actuality I should have received payment instead. I am unable to figure out how to rectify on my end.  Need guidance or a fix from your end.