Xiaomi India - Warranty not accepted by service centre

Bought a xiaomi mobile phone in december **** which is still under warranty. There is a fault of network droping with device. Went to service centre with origional bill and device. They checked the device and told there was a mother board issue and it will not come under warranty because it seems like liquid damage they tried to show alkali but when I see there was nothing like that only I had to accept because they were telling I could not see anything what they were saying. They just didn't want to change that expensive part under warranty so they refused the repairing the device. Moreover they charged Rs.*** to check the fault. So upset with mi service center and company will never buy or suggest anybody to buy any item from them.