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Not a scam at all. This is Apple's policy. There are certain things they will fix like the screen or battery, otherwise the will generally replace it. And there is a cost related to that if your phone is out of warranty. Maybe try calling Apple Support and talk to them directly. Maybe they'll agree that a replacement should last longer than 4 months and do something for you. Worst they can say is you have to pay, which is where you're at now. Apple has been known to do some pretty nice things for people. Just talk to them nicely is my best suggestion.