With all these doubler sites that claim to do it I don't think it keeps paying because of the last few that joined will lose out by not getting paid when they close up shop as they always seem to do when they want to run away will all the investors funds. 
That doubler sites or ponzi things is really risky for doubling bitcoin, they can easily scammed your bitcoins. My advice is don't invest on ponzi like that who claim can doubling your bitcoins.