Help redeeming Christmas stocking choice voucher from Red Letter Days

I bought a Christmas stocking choice voucher during December last year and want to make use of it at Gordon Ramsay's Street Pizza. Upon checking where I can use it after logging in with my voucher details there is no mention of Gordon Ramsay's Street Pizza. I had a live chat with Buyagift who said firstly my voucher is only worth £15 and secondly if Gordon Ramsay's Street Pizza isn't there you cant use it. Anyone had a similar situation?

It was related to this deal: hotukdeals.com/dea…788