Nishant Infotech - Mobile servicing-data lost

I had given my Redmi *X phone for damaged display today at Nishant Infotech - MI service centre, Borivali East, Mumbai. I was told data backup was not necessary at the time of submitting my phone. They said it would take * */* hours to repair the phone. Two hours after submitting my phone my family received a call stating that the data format would be required and all data would be lost. The phone contained important data which was lost due to the carelessness of the staff at the service centre. When I rushed ti the center and protested, the staff all ganged up and threatened me and i had to shout that i may have to call the police. I need your help in addressing this issue. I am terribly distressed the way I was held to ransom by the service centre guys. The service centre is run by Nishant Infotech and the centre manager is Poonam Singh. The staff was extremely rude and intimidating. I had spoken to few people who were sitting for their turn in the centre. They said that this is normal way of behavior of the centre staff. They think they are the lords and fleece the customers giving arbitrary defects. I had gone to replace my damaged display and was told to replace speaker holder and charging socket too. Otherwise the warranty cannot be provided. Moreover they formatted the mobile even after they had confirmed that the data backup was not necessary while accepting the mobile handset for repair. I was helpless with all this. The level* escalation was the centre manager who was also rude and threatening. The level* escalation email id bounced back. The level * escalation was an email id shivkumar@xiaomi.com to which I have sent an email. I am enclosing the service slip and their bill for your reference.