Quest for a Windows7 refund in the UK - laptop upgraded to GNU+Linux

Hello Everyone

I have been trying to get a refund for the un-used/un-registered 
Windows7 which came with my Acer laptop. The retailer indicates only 
AcerUK can refund. Purchased on 6 Jan, I've been communicating about 
refund since mid Jan.

Unfortunately AcerUK will only refund their cost (they said approx €30) if:

A) I post the laptop to Plymouth at my expense.
B) They wipe the HDD themselves (well.. already has Ubuntu on it now as 
it was wiped by me).

I kept a few photos and records as I went, AcerUK indicate that is 
insufficient.

If anyone has any suggestions, or examples how it has been achieved in 
the UK before I would love to hear.

I found this old case, but was purchased direct from Dell:
http://news.bbc.co.uk/1/hi/6144782.stm

Best regards, Jon