not taking responsibility

I took my phone back for repairs after using it for a month & a week then after a month a got a cal saying they can't fix it due to liquid damage,bt it didnt fall into water.they said I need to pay 1500 so they can fix it & I refused & told them to return,BT upon its return my phone had dents all over it & I refused to take it back because when I returned it it was still new,without dents.now da shop is refusing to take responsibility & they confirmed that when thy sent the phone for repairs it was okay without any damage on it.I want my phone without dents and I will deal with da liquid damage.I will go public with this because no1 is willing to help me.both da shop and da area manager.