Why won’t my £100 Ticketmaster gift card work?

I wanted to book a trip to the theatre but the card hadn’t been validated so I couldn’t use itFor my 70th birthday last year, three friends clubbed together to give me a £100 Ticketmaster prepaid card so I could book some theatre tickets and, at the time, I was delighted. Ever since, we have been trying to use this card but to no avail. My more technically literate husband tried to validate it according to the instructions. When that failed, my daughter-in-law had a go. Ticketm