Should I continue using this Bitcoin Doubler?
It is definitely a scam. They typically pay people who paid in before with the payments of the people who pay in later. This is unsustainable and it will collapse leaving those who paid in later without any money. Furthermore, most of them will simply take your money and leave. This is a scam and so is everything that promises absurd rewards. This includes doublers, HYIPs, ponzi schemes, etc. You pay in at your own risk and if you lose money, then that is all your fault and there is nothing you or anyone else can do to get your money back.