Uhh, either give up or fake it out? I mean, Bitfinex completely has no fault in banning your account ngl. You should've already known that using Bitfinex in Cuba is not allowed and even if you didn't know, just signing up would have brought about that warning already stating that you can't use Bitfinex in your country, but sadly it came up now after you already have your funds inside, that means you were partially or maybe even fully aware that what you are doing is against their ToS. If you do indeed decide to give up then that's that, but if you don't it's either you fake it out or just find someone to help you fix this, butnot here I suppose. Not really the best place to look for help with regards to faking documents imo.