One Plus — Service centre not repairing product in warranty

I purchased oneplus buds in decmber 2020 and after using it for 2 month the left earbud stopped working and is unresponsive .i registered a pickup for the service centre at indore and my deviice was picked the company wated a ainvoice and i sent them but the service centre executive did not accepted my requests statingg that the device is not purchased from authorized store . after continuos requests also they refused to repair the device which is in warranty.and so here is the complain