There are a number of issues here, one being that the item was purchased by your partners dad,so is the item or warranty in his name or your partners name. The other is that it would appear it is you and not the owner who is conducting the dealings with the repair centre.
It would also appear that the power lead might have been sent with the item, and this is now missing, so another one as been ordered. Normally it is not a wise move to send items like power leads, software etc, because the repair centre will use their own, and perhaps discard the customers, which may well then be lost or unaccountable.
I would suggest that you contact Consumer Direct http://www.consumerdirect.gov.uk for further advice.