they steal my bitcoin. What to do in such case?

When someone steals something from you, the appropriate response is to report it to the police. You'll have to provide evidence that a crime has occurred.

If the evidence is not the sort that would be credible in a court of law, it may not be possible to progress this.

If the criminal is outside the jurisdiction of your police, and the sums involved are low, it may be difficult to progress this.

Due Diligence

Part of the intent of cryptocurrencies is to create currencies that are outside the control of governments. A corollary to this is that you need to be diligent when assessing the trustworthiness of cryptocurrency organisations

See

• Computta Review: Hand over the keys to your PC to persons unknown
• Computta – Smart Cryptocurrency Mining PC Application Software?

Computta is made by a company named Computta Networks LLC. The corporation started appearing online in July 2017. They claim to be registered in Delaware.

There’s virtually no information about the company available online. In fact, one of the first results that pops up when you search for Computta Networks LLC on Google is this page on RealScam.com, where the website is identified as a likely scam.

There’s also the problem that Computta’s testimonials are accompanied with stock photos that have been taken from other websites. They do not appear to be legitimate testimonials.