Threat of termination

I am working for last 4.5 years as Executive Assistant. Around 4 months back my reporting officer resigned and new person hired in his place. Within these 4 months, my new reporting officer appointed a new employee in same designation i.e. EA and told me that she will also work and I have to train her in work. After one month of working with the new EA I have been suddenly told to resign otherwise they will terminate me. And this month appraisal also have to be done and I have not been given any appraisal. In this regard I would like to mention during all the working span there is no complaint of my work, personal behaviour, punctuality nor office decorum or etiquettes. And for the appraisal period new reporting office could review only for 2 months only as far as I know. Since the day of threat of termination no work has also been assigned to me, without my knowledge my system and office email id has been blocked. I am sitting idle, without work and without appraisal. May I know what I can do in this regard. How strong my case seems.