It sounds to me that you try to book on a us webpage and they are just blocking Cuba. Cuba is not existing on webpages based in us. Try to book on european or canadian or south american webpages. The nh Capri, one of the best hotels at the moment in HAV, is available next week for around 80 eur. Mansion Xanadu in Varadero costs next week around 80 eur, which is a steal.