The lesson learned here is to never do a new add on for free. If they have a new conny etc then charge more. Simple.
This is the thanks you get.
Just email them a statement of account and ask them again
Statement of account 
it doesnt happen too often but if a customer queries how much they owe me then a statement of account either emailed to them or printed out and pushed through their door sorts it......
i sure some customers think i dont keep records!
