When you engage in a 'long distance' relationship .. Especially as a child, there are many things that you (as a child) may not catch in terms of what you are being told.
Either he is in what he legitimately says he is in "an abusive situation" with his foster mom .. Which, BTW, he needs to report to his child care workers .. Not YOU .. OR .. He is not in being legitimate at all and is completely lying to you in order to gain your sympathy in attempts to manipulate you. I'm not sure how this mom can even 'block' you without him 'unblocking' you. THAT is suspect all on it's own.
I am curious to know if you have ever met him in person? .. Or are you just going by what he is telling you on line? THIS could potentially be something other than what you've been led to believe.