I was googling on any free services like SauceLabs Cloud and i could not found any of the free services. All are paid services or trials. So is some one using any free services like SauceLabs Cloud where i can run my selenium code on different browsers and devices?
There ain't no such thing as a free lunch also known as TANSTAAFL.
Somebody needs to pay for the servers and salaries for people managing them. For all "free" services you use (gmail, facebook, etc), you are not user - you are the product. Companies provide you with free services, so they can sell your info (and anything you can glean about you, your interests, hobbies, friends etc, from how you use their services) to advertisers and whoever pays for it for whatever reason.
Automated tests do not care about the ads, so so their "attention" cannot be monetized. Just the opposite is true, companies providing "free" services spend effort to make sure that their customers are real humans, not robots - see CAPTCHA.
Browserstack - Paid one but providing the Free trail.