One year gift is lying

Good day. I was Given a midweek voucher after they told me on the phone that I can choose between a midweek or weekend I did told them I want the weekend because I have children in school then they told me the weekend voucher is finished but I must take the midweek one I can just phone one year gift and they will exchange it for me to a weekend. today I phoned one year gift and I asked him can he exchange it for me for the weekend 1 but he told me no they can't do it. so now I can't use this voucher.