I received a £42 rail travel voucher as compensation after a long delay in January. I'd now like to use it to buy a Gold Card discounted return from London to Didcot Parkway, a return from Didcot to Swindon, and put the balance of the voucher on to my Oyster card. Would I need to do this in a single transaction, or can I get change issued in the form of a voucher? And if so, can you recommend a ticket office that would do this, as I think most National Rail ticket offices do not credit Oyster cards? Many thanks.