Hello friends I am using redmi4(black). It's only 3months old. I protect my phone using a back cover. But now I noticed that there is a lot of stains on the side part of the black body. How to fix it?? I tried many cleaning agents but the stains donot disappear. Please help me .... please suggest a way to clean this stain?  Can I replace the whole phone body using warrenty?? without any cost??