Last Minute.com Nightmare

Worried of Wiltshire! Can anyone help? I have just booked two tickets for Blithe Spirit at the Gielgud Theatre in London for 23rd May with www.last minute.com – they don’t sell allocated tickets and after ringing the theatre to enquire about allocation I was advised by the theatre to cancel with last minute.com and rebook an allocated ticket with the theatre.
My problem is that I am taking an elderly relative who cannot manage stairs so we need allocated tickets.
Lastminute.com REFUSE to return my money.
I called 5 times and was cut off every time. Finally they said they would contact the theatre to get their permission to refund my money and get back to me in 24 hours. Will they? Watch this space.