can trial user change mac address and use the internet again !
yes
How can we Prevent that
Any Suggestion
You can’t unless you directly control the clients computer.
Require an email sign up with radius. Sure, they can create multiple email accounts but it would at least add some work to their efforts.
For smart phone cant we using another thing instead of mac address for authentication
yes - user name and password 
HHHHHHHH , you know am not talkink about that
i need to use trial with more security
You’ll need to “think outside the box” to achieve this, eg disable trial user function and on the login screen publish an account that is restricted down. You can then control the account better.