Customer Balance but no open items

We have a problem where, during Euro conversion, a customer's account was not handled properly. Now, each year we have a balance on the customer account but I have no outstanding open items. I want to clear this customer account and close it but can't. I cannot reverse the problem documents as they are pre-EURO conversion so the system won't let me.

If I do F-02, F-32, F-30 etc it clears the balance but I get left with an outstanding open item. Once I process the open item, I get the balance back. I need to clear the balance. Anyone got any ideas how I can do this?

I'm in 4.7

TIA

Mitch