Unhappy

This morning they were running a special on buy1get1 free tickets for the MetrofmHeatwave in East London so I bought the tickets now when I went to Computicket to print the tickets i was told i can only get one so I called and followed up with them only to be told that I should have clicked a certain button of which by the time I was purchasing the tickets that option was not available its only available when I check now now they are refusing to give me my free tickets whereas the fault is on their side and on the website it does state that the Black Friday deal is available