24 white roses died in 3 days disgusting!!

I had 24 white roses delivered as a present for my birthday after 2 days they were brown, 4 days they were hanging lifeless.
I rang inter flora and told them about the flowers as well as emailing them the pictures of the flowers and that I was upset. After 4 days I received a email saying they were sorry and that they've sent me a £10 E-voucher to spend with inter flora. I'm disgusted that they offered £10 voucher and rang them back saying I wasn't happy about this and wanted a refund! They didn't get back in touch with me for a week so rang them again to be told that someone was looking into it an will get back to me which they didn't get back they rang my partner who bought me these flowers and told him that all they could do was refund £20!!!!
I'm Disgusted that inter-flower are happy to take £100 but not happy to refund or even replace the flowers WHICH inter flora say there flowers have a 7day guarantee!! Sorry inter flora but £100 is a lot of money for flowers and I EXPECT FRESH BRIGHT FLOWERS!! If only I could put pics on to show!