redmi band - No repair and No replacement

I received Redmi Band as a gift ordered on **th September **** through Amazon. After using for four months, it suddenly stopped working. I visited Xiaomi authorised service center. They said within * months of purchase, the watch has a replacement warranty but no repair. As my watch was under warranty period, they refused to replace stating it has some scratches on the side. So now I don't have any option, neither watch can be repaired nor replaced. I have used the watch with those scratches, then why do they have issues with replacing?