Help iPhone 7 plus Jet black owners?

Well, i bought iPhone 7 plus 2 weeks ago and since then i kept it in flip cover as apple mentioned that its easily scratchable. And today i removed its cover and saw from backside's upper and bottom side (antenna area's) shine is gone and there's some thing which can't be cleaned and easily visible and not looking nice. I don't know what to call it but there's some dirt i guess or it looks as if paint is removed so my question is how to get and maintain the shine of jet black color? I like to keep my phone clean and never had any problem before with any phone. I feel like I shouldn't have chosen this color because this happens in 2 weeks (even in its case) and what will happen in near future and no one will buy it when i try to sell it to buy another phone even if someone will buy but they won't give me good price. Sorry for my bad grammar since my language is not English i tried my best to explain it to you and now expect you to respect me and give me a better solution. Kindly reply and, Thanks in advance.

Here is the problem, if you use a loose fitting case, pocket crude can get in behind it. Just handling the phone, in and out of pockets, will case the case to flex, and rub some of that lint/crude into the case in spots, dulling the finish or even removing the paint. What you should do every so often is take the case off, clean the phone and the case to remove an crude, and get a better fitting case with a soft inside where it touches the phone.

But even with a soft shell touching the phone, you will still want to clean it out, cause the day you forget and go two weeks, there will be more rubbed dull spots.