Jewellery — Gold ring turn into blackish colour from one side

Address: Anand jellelers, indore

I have purchased one 22kt hallmarked gold ring from anand jewellers. Now within 3 months it loosed it's yellow finish and turn in blackish colour at one side.
Now what to do, where to complaint about it. And what should be done in such senerio, I want to return it and get my valuable money back, as it is looks like fake one.