Xiaomi India — taking money within warranty period

My redmi4 mobile is suddenly off and while turning on only loading appears and hang on the screen. Today i went to servicing centre they said water inters through headset and my motherboard is not working. They force to sign a paper for repairing in out warranty and asked me to give rs 800. The phone was of only 6 month and neither through water nor broken. I don’t want such unlawful reason in innocent customers. I refused to give the money and came back without my phone. So where is our warranty from company. Take action to the officers concerned in this problem. My number - [protected]. Mail - [protected]@gmail.com