I suggest investing on some legit and trusted bitcoin doubler websites. You can find some in this forum which you can trust because many of the users are being paid by them here.
but most sites bitcoin doubler using a ponzi system which means it will not last long.
Exactly! All those doubling sites are scams. How can you double anything in the short period of time as they promise? They only want your money from which they'll maybe return you a part.
It is why with my investment system you double in a longer time...
And you are sure to get profit after 100 days...