GST on delay payment interest

Yes if the party is not paying the GST amount, you treat the basic amount as inclusive and discharge tax thereof. 

You have already raised a debit note with basic amount 100+GST 18, but couldn't collect the GST amount form the party. Now you treat the basic amount as inclusive and discharge GST. Nowhere RCM is applicable.

Now my question is why you want to raise a debit note again?

Debit note is required to be raised. Total amount=amount paid by the party. Basic and GST figure, you back calculate and put.