If you just got it, it should still be covered by the manufacturer's warranty.
Contact the retailer that you bought it from as ask if you can see another similar model to see if it has the same problem or not. If the other similar model doesn't have the same problem ask the retailer if it can be exchanged due to the fault. If it can, factory reset your phone before you hand it over to delete your private information. and remember to remove the SIM card and SD Card (if any installed) Also take the sales receipt (or proof of purchase), the charger and any other accessory that came with the phone back with you if you can exchange it for another
Some will help and others won't. It depends on the store policy regarding warranty service.
Remember though that the phone is always covered by the manufacturer's warranty regardless of what the store says. You just may have to deal with the manufacturer and not the retailer.
If the retailer doesn't want to help you then follow the information in the warranty statement in the documentation that came with the phone as to what you have to do to make a claim for a warranty repair or replacement.