In the AR Aging Summary report, when a name shows 0 under Total, you know that name should not show at all. Their Math is 0, but you have unapplied transactions. You double-click their total of 0, to see what is Unapplied against each other.

Go to Receive Payment for that name. Leave the Amount as 0. Here you can select anything that is an open charge balance, and here you see the Icon in the ribbon at the top to Apply available credits, as shown in the middle bottom part as value still available. Do this until everything is Applied to something else. Always leave the Amount in the Receive Payment screen as 0; you are not Receiving any new funds.