Redmi 4a by MI - Got the faulty mobile online from Amazon

I have purchased a MI Redmi *a mobile from Amazon.in on **.*.****. I was facing hanging problem. I visited MI service centre and update the mobile software. After some days I noticed the same problem. I went to service centre again and they said that it is the problem of main board after changing this board you will not face the hanging problem again. They have changed the the main board on **.*.****. After changing the main board the problem is still there. I have visited the service centre again and they are not responding properly. They again updated the software on **.*.****.
The mobile is faulty and after changing the main board mobile still hanging. I have to visited the service centre again and again for this problem. Please replace my mobile or refund my money.
I have attached the job sheet in which it is mentioned that main board has changed and again i had to visit service centre for software update.