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I was phoned by a person from Blackwater Global, introducing themselves as a professional broker, and I followed their advice and bought some shares (US company shares). I then decided I wanted to sell and asked them to sell them, they are now giving me a problem and say I have to pay in more money before they can sell the shares as they bought them as an institutional block. What do I do at this point.  does anyone know of someone I can talk to about this.