Can FCI deny posting orders after issuing Appointment Letter ?

FCI asked me to join duty on or before 30/9/14 - I joined duty on 30/9/14 after giving my Joining Letter - FCI has not issued Posting Orders and after 15 days they asked me to wait until further orders from their Higher Office as they are forwarding my case to their Zonal Office. The gist of my case is given below for your easy understanding. A case was booked by my wife under Sec. 498a, 306, 3&4 DP Act - I arrested and released in May, 14. I selected for Technical Grade III Assistant in FCI thro' Staff Selection Commission. I mentioned particulars of my arrest and case pending in Court in the Personal Forms supplied by FCI in July 27th 2014. FCI asked me to take time to submit the final report from Police. Accordingly i asked time for 6 months. In the mean time My wife has given an affidavit to FCI stating that we are compromising and withdrawing case at the time of 1st hearing of the case in the court. FCI permitted time and asked me to join duty on or before 30/9/14. I had been to FCI Office and given Joining Letter on 30/9/14. But they have not given me Posting Orders. Today the FCI told me that your case has been forwarded to Higher Office for their advice. My question is Sir, Once the Appointment Letter is issued and Joined the Department, can they take back their decision. AND if that is the case what steps I will have to take. For immediate relief shall I apply for Compromise Suit in High Court. Kindly let me know, I want to proceed with you.