Job Termination of Senior Manager (Supervisory position)

Dear professionals I am confirmed employee, and company had terminated my job on performance basis. Working on supervisory position (Sr.Manager) 1) Company terminated me on 16-Dec-16, with three months pay. 2) On 15-Dec-16 I marked the email to HR, for asking reason that I am voluntary willing to resign and wish to serve 3 month notice period. 3) Till date they have neither taken my acceptance on Appointment Letter and not issued it. 4) From 17-Dec To 19-Dec I was on sick leave, I applied leave on 19-Dec on email and its approved by my line manager on 19-Dec. 5) No written notice served, only one email received that you have not achieved your target. They assigned half of the company monthly achievement Pan India. And asked me to improve my performance with higher target. 6) No performance improvement plan issued 7) No reimbursement paid for last 6 months 8) I have their laptop due having copies of email. No they are asking to return. 9) Company is not performing for last 8 months that's why I voluntary willing to resign. I AM LOOKING FOR RELIEVING LETTER + CANCELLATION OF TERMINATION LETTER. Please suggest action. Yagyaa