Thanks for your help.
Basically this workflow is on pause status and the workflow supervisors have been receiving notification emails everyday. So they wanted to shut this workflow down completely.
Option 1 and 2 are not working in my case, because whenever the workflow is selected it crashes the client console. Hence I have to do it from the backend.
I also used xtk.worfklow.Stop but it didn't work because the workflow status was changed from 'paused' to 'stop requested' and then back to 'pause' again.