I've been working for a startup for the past year, and I resigned from it last month. I served the notice period, and after my last day of duty, all of my accounts were disabled. I tried contacting my manager. Initially, I was told that it would take a few days to provide a relieving/service letter, but later I was straight up denied, citing that my performance was not satisfactory and that I'm not eligible for any proof of employment. During my tenure, I received a 20% salary hike within one year, so I don't believe the performance issue holds up well. What could be the remedy?