Just to update on this - If you have any old tickets with a customer reference number on them, they will accept that. Thankfully I've purchased tickets from a couple of different addresses in the past and with my parents references managed to get the 5 tickets i wanted! I can't believe how difficult it was though. I couldn't do it on the phone, so my mum went to Villa Park and they found enough references to our addresses!
Last time my dad went to an FA cup game on his birthday we beat Arsenal 2-0, so hopefully his birthday luck will continue!