Thanks for getting in tocuh with the Communiy, susanhepa.
Since you're seeing credits for customers on your A/R report, I'd recommend making sure any customer credits that need to be used are applied to their appropriate invoices.
Here's how:
In your left navigation bar, use the + New button, then choose Receive payment.
Specify a customer in your Customer drop-down list.
In the Outstanding Transactions section, pick which open invoice you want to apply their credit memo to.
In your Credits area, pick which credits you want to apply.
In the open invoice's Payment column, enter how much of their credit you want to apply.
Leave your Payment method, Reference no, Deposit to, and Amount received fields blank.
Enter any necessary information requested on the form, including its Payment date.
Confirm the total's correct after applying the memo.