Rules of Resignation in Govt Banks

I was working in Corporation Bank since 1999. In 2004 I got married and asked for reqst transfer to Bangalore. They kept my request in waiting list. In July 2005 I had an abortion due to not stress n heavy work. Again I convinced in Dec 2006 again I conceived so I never wanted to take any risk and doctor also advised me to take rest for 1st trimester. I was on leave since November 2006 in Dec I wrote a letter to bank, in that letter I explained in detail about my health and pregnancy and asked for Request transfer, lf it is not possible then consider this letter as my resignation. In March 2007 they accepted my resignation. In between these three months neither Management nor Union nor my Branch manager approached me or did any proper enquiry nor cross questions nor available ML nor sanctioned LOP nor gave me other options. Now some days back I read about reinstatement process. And no company can fire pregnant woman. Bt how come my Bank considered my letter as resignation? Is there any chances or hopes to get it back?