Registered supplier of Service issue invoice without charging GST?

Mariappan (Student CA final new) (106 Points)

17 December 2020  

One MY Supplier of Service (AMC Service Providers) Registered Person on July 2017- issue invoice without charging GST form Sep 2017- Mar 2019. Now Dec 2020  is gst department ask him for he is liable for Pay GST on that service provided in that period sep 2017- Mar 2019. Now the service provider ask me the gst for the relevant period . i am not ready to pay because if i paid i am eligible to claim ITC? how can we resolve the issue?