@purnachander could be an issue with a bad battery or the USB charging port. Start with a new battery. Since iFixit does not yet have a specific guide for that, use something like [https://www.youtube.com/watch?v=DPWXe0MnULs|this video]
If a new battery does also not charge, check the charging port and measure the inputs with a multimeter. These headphones are no fun to work on but it can be done. One step at a time.