Please address an email to the HR head, your immediate senior, your departmental head, the Company MD and/or CEO, and CFO, clearly stating that you are pregnant. You are aware of your rights under the law and hence, under no circumstance, willing to resign.
In case the matter becomes severe, please visit the link below and log your complaint:
http://ncw.nic.in/frmLegalUnit.aspx.
If you need any paid legal assistance, please let me know. I would be more than glad to help you with appropriate resources at the lowest cost.
Regards,
A&B