Lenovo — zuk z plus mobile

Address:

560016

I had purchased lenovo zuk z 2 mobile handset (9 months old) the mobile had heating problems and one the day while using google maps the handset had heated very much and switched off. I let it cool, after some time tried to turn on it never worked.
I took it to a authorised service center located in indiranagar, and they took the mobile (After physical check) saying its is covered under warranty. After two days i enquired the status they initially said they are waiting for a spare. Then after couple of hours they called me and said there is a damage on the mobile which voids warranty. I went to clarify the same they had opened the casing and they showed me a couple of dots on the rim.
I asked them that the mobile was checked while recieving for service now they say there is a damage. They said they missed to notice such tiny dots before.