Never experienced to scammed on bitcoin doubler sites but I have many experiences on cloud mining sites and investment site that related on Crypto.

All of them are all the same that they promise to make your investment double but after that, they run all investment of all investors.

Did you hear about scrypt.cc and coinsera? I can't forget these 2 sites because I thought that the site can give me a real profit and passive income while my bitcoin stuck on their site. I experienced to withdraw on their site in the first time so I encourage to invest more but for the 2nd time my withdrawal never arrive and it's stuck forever.

Now, I learned to never invest in any investment sites and doublers there is no free profit online(except for holding crypto or Buying a miner) because those sites are useless and own by scammers.