Lava Mobiles — Phone doesn't function properly

Address:

Thane, Maharashtra, 401202

I brought a lava arc 225 model on 7/7/16.
A basic model. my complaint is that when my phone is on silent mode it does not vibrate.
There is no vibrate option on my mobile.
I addressed the same to the shop keeper and the customer care service centre too but. they refused to change my phone.
There is no description on the mobile cover too that the phone doesn't vibrate, so how are we suppose to know the same?