Harry Gross: Somebody screwed up

Dear Harry: I'm in an unbelievable situation. I'm enclosing the correspondence so you can see for yourself. I bought a refrigerator-freezer, clothes washer and dryer from Sears. There were some problems with the washer and they replaced it. I charged all of this on a Sears card that's backed by Citi Bank, and I paid it off in December 2009. Since then, they have been on my neck for payment of $1,888. They have seen my canceled check, but they now claim that I owe them $1,000. Sears tells me to contact Citi, and Citi tells me to contact Sears. I have made dozens of calls and no person will offer help in getting this straightened out. They insist that the money is owed, but they won't (or can't) tell me what it's for. I did not ever use that card for any other purchases. I don't know if this has affected my credit, but that's another matter. How can I get these people to see that I'm completely paid?