Sony not given proper warranty information

Location/place: Pune

Name of company/service: Sony Mobile

I bought a Sony Xperia Tipo on 28oct2012 with 1 year warranty. Recently my phone stopped working, I went to sony service center and ask them to repair my phone then they told me that warranty of my phone has gone void. I asked them why then they told me about the litmus in y phone which was red. They told me that litmus gets red in contact with moisture and warranty lapses if litmus is red.
My concern is that I remember very well that litmus in my phone was already red when I bought my phone.No one (dealer and company) told me that litmus must be white while you purchase a new phone. They only told me that don’t accept the phone if the seal of box is broken. Once you break the seal the product is yours and they cant take it back. So now my question is that how can a person check for white litmus without knowing anything about litmus in the phone and without opening the phone which can be done only when you tear the seal of box.