Employer asking backdated salary after doing backdated exit in the middle of notice period.

I have resigned from a software company having 3 month notice period. In the mid of notice period they released me from project and ask to submit laptop to different building and revoke access of current building. I got little bit confused so i started communicating to HR to suggest on my last working day i.e. project release date or some future date. First one HR replied, that reliving letter cannot be given as your last working day in the system is next month. After sometime another Senior HR replied on the same email that they will do backdate exit in the system according to my project release date. She replied that as you are not reported to work after project release so they were doing backdated exit. My team mode of working is mostly online and I was also following the same. As per instruction, I have submitted the laptop also. Additionally, there was no instruction or new work allocation given to me. I don't know why HR is repeatedly saying that i did not report to duty, however I immediately start conversation with HR after submitting client related assets so that they can guide me in a better way. Please guide me on this issue as now company is threatening me for recovery via legal proceeding if backdated salary not paid immediately.