Damaged phone

I recently bought a phone from tech trader<br> when i got home i noticed the phone's battery is shaking inside<br> i took the phone back the following day<br> <br> they then came back to me and told me that i dropped the phone and they told me that the phone was a demo and therefore there's nothing they can do,they told me that i have damaged the device and im trying to claim for a new phone<br> <br> i cannot believe this after paying so much money for the device to be treated like this