Recieved Legal Notice from TCS

My sister joined TCS in June'25 but on Aug'25 HR team asked to resign for a silly reason of using chat GPT. HR team clarly mentioned there will be no deductions and pay backs but after one month TCS sent an email to pay exess salary of 11k. For which we tried to reach out HR through emails and calls but we didnt get any response and the ticket raised in th portal was closed without any response. Today my sister recived legal notice asking to pay the 11k or face the legal issues. Kindly suggest what should be done here. Location: