Payment not received

[dotnet]

There's a notification on the left of My eBay page telling me of things I sold and the total I earned. Underneath these is 'Not received... £20'.
For the life of me I can't think what I sold for £20 but wasn't paid for. My list of sold stuff only shows the last 60 days, and this 'Not received... £20' thing has been on my screen for a while. Obviously my Paypal history isn't going to help because that's stuff I received payment for. There's nothing I took a cash payment for when I'd expected a Paypal payment, - so it can't be a mix up over cash and Paypal, I think.
Does anyone have an idea how I can work out IF I really am owed £20, and how to find which item it relates to? Thanks - I'm mystified!

[iggy155]

Think the best thing is to speak to Ebay customer service.