Regarding extension of joinning period!

I, Shyamaprasad Bhattacharya, used to work for a Public sector general insurance company. while working I got an opportunity to join WBCS gr A services, under the department of Food and Supplies. I received the appointment letter on 7th of September 2015 and resigned from my previous employer with immediate effect on that very day. The appointment letter asked me to report within 7days, which was impossible for me as I was not even in Kolkata. Though I came back and met with the concerned officers and was suggested to submit a prayer for extension of joining period. I did submit such prayer on 14th of September 2015, asking for an extension because there are many issues regarding clearances and release letter which generally takes 30-40 days, including the notice period of 30days. Now today, 7th October 2015, we (similar people with other jobs) started receiving letters, dated 24th Sept 2015, from Government department that we have to join immediately. Unofficially we were told that they will terminate our appointment right away if we don't join immediately. Its an Gazetted officer post, what is legal support we can avail? any law will be there by our side?