Can I get a refund on tickets?

I purchased two tickets for the Riverdance matinee in Manchester this coming Thursday for my Grandparents.
My Grandad has taken ill with a bad back and its looking unlikely that he will be able to make it to the show.
Ticketmaster policy states they will not refund tickets.

Does anyone know if Ticketmaster will budge on the refund policy - or is it worth contacting my credit card company to see if I can claim anything back from them?

Its a lot of money to lose if my Grandparents cant go
Many thanks
Laura