messages are being sent which I am not aware from my I phone leading to deduction of balance
It's best to contact your carrier for information about charges. They will know the specifics of your contract and options as well as help you by asking some questions like 


What version of iOS are you running? 
Are you using iMessage?


Your first step might be disabling SMS on the iPhone and then contacting the carrier to get further instructions. It really depends upon what number is sending the SMS and if you opted in to any subscriptions or got crammed or signed in to SMS on a web service of some sort.