People paying at the SCO with benefit cards and leaving a balance unpaid.

We have had an ongoing problem of people buying like $15-$30 or so at the SCO and they swipe their UHC or Humana Health Benefit Card. It will pay part of the bill. Then they walk off with all the items while leaving a balance on the screen. It's usually less than $10. It makes me so mad! We've tried to void off the least expensive item that looks to be unpaid. The X by the item is dark gray. Sometimes this works, but many times it doesn't. We have to CANCEL the transaction and the benefits are refunded to their benefits card!!! I am sick and tired of these scams. We've confronted customers and they say, "My benefits card should've paid for ALL of that." NOPE! It didn't! Some customers come back. Other customers act like they don't hear the SCO host calling to them to come back. We make notes for AP, but I don't know what happens after that. This is stealing and I'm tired of it.

Are many stores having problems like this? What's the answer????