Not that I want to labour this or anything...had a nice call from a very helpful lady at the PO helpline a few days ago - asked me to fax over any receipts I had and also took my debit card number. Spoke to her a few days later and the records had confirmed my debit card payment. Now they need to confirm my credit card payment and can then issue a refund. Gave the details.
Phone call (sorry, message left at home - why? all other calls have been to work) saying they can't trace my credit card payment (the one I have a receipt for...) and I need to ring them with further details on Monday. I now need to print off a credit card statement (just done!) to prove the payment was taken twice.