Similarly I had to get a refund on a 10-pack of items when I only received a 5-pack. Months later I get an email saying I didn't return all 10 that I had ordered.
I once ordered a rail of Atmel Microcontrollers from Digikey. Got four 74HC00's. Called them, sent them back. And then Digikey sent the $28 bill to collections. I complained and they politely told me to fuck off.