Xiaomi India — Mi 3s cellphone

Address:

Pune, Maharashtra, 411036

I am using mi 3s mobile, purchased on 30th December, 2016 which is under warranty. IEMI is [protected] and [protected]. I am facing consistent hanging of phone while using any phone app or any other social app since 2 month s. I need to know why it is happening in brand new phone. My phone stops responding whenever I use internet or apps which supports internet. Please replace my phone or else solve my problem as soon as possible. If not solved then I have to take some legal actions against the company.
Please revert and assist me as soon as possible.