I bought an iPhone 6S Plus in November 2015. In the back and near the sim tray there are several rust marks. I used a back cover since day 01 so I couldn't have scratched the phone nor matter what. Was there any other cases like this? Would Apple replace my phone? I only have the 1 year warranty they provide with purchase. On another note, does apple cover accidental screen damages for free during the 1 year warranty period or would i need to buy a apple care protection plan?