GST ON ROYALTY PAID TO STATE GOVERNMENT.

My firm has received a notice now from the cgst authorities for paying service tax (rcm) against royalty paid to Government for mining activities. Period is from 01/04/16 to 30/06/17. Next comes gst. The same situation is here also. My item is china clay , taxable @ 5% I had no service tax registration. I have never paid gst against royalty . CBIC website is saying that I should pay rcm @ 5% against royalty paid for mining activities. Cases are pending before Supreme court in similar matters. What to do, please suggest.