Asus India — Service issue

I have an ASUS mobile AZZJ01. i gave my mobile to F1 info Solution & services Pvt. Ltd. in Anna Salai, chennai, Tamil Nadu, India (asus authorised service center) for service. My mobile have two USB charging port. One of the port got fault but another port was working fine. I gave the phone to repair the faulty USB port. but the service centre made the main to board to short circuit due to negligence. At first they asked for 800 but now they asking me to change the main board cost rs 30, 000 and made my mobile to dead condition. i need my mobile back with the same working condition while giving at the time of service. I still now not got my mobile back. i have the service form with me. if I am not getting my mobile back with same working condition. i will file Consumer complaint in court.