Xiaomi India — mic not working properly

Bought redmi note 4 via flipkart on 6th september 2017.

1 the voice (Audio reception) very slow during a long call and the receiver is also unable to hear the conversation at one audio level, as usual i thought it is net work issue and ignored. But the problem continued to persist even with good signal areas. This was checked and confirmed by your customer service.. Technician also change software but there's no result. Now same problem found as previous