employment rules regarding

respected sir my question and situation is really chaotic(please mind the dates carefully) i asked this question to many lawyers but unfortunatelyno one knows law regarding thisand their answers shows that they are also not clear with rules...... sir i had been selected for the post of sub inspector in cisf final result declared on 25/04/2014 on ssc website and got offer of appointment dated 8 august 2014 from cisf nisa ,hyderabad for joining on 13 september 2014,.. now i have been also selected for the post of sta 'b' in drdo through ceptam examination whose result is declared in the month of june 2014 on and got a letter from them dated "31 july 2014 " stating i have been reccomended for appointment to a lab say xyz and have to send attestation form alongwith acceptance to the xyz lab then they will do the pre appointment formalities and issue me offer of appointment if everything is found in order... now situation begins i have opted to join cisf on 13 september 2014 for training and didn't responded to drdo letter after sometime i found that cisf job is not good and i doesn't felt comfortable their.. at that time i got a letter from the xyz lab that reminding me to send acceptance and attestation form in next 15 days sir.. i choosed to join drdo i sended them acceptance letter alongwith attestation form .. in that form in jobs column i mentioned that i am working from 13-09-2014 in cisf xyz lab sended police verification to my house .. police also verii m in cisf from 13-09-2014 they also sended verifiction to my office in hyderabad asking for my character and whether i will be releived from the organisation or not my department said that i will be relieved .. as at the time of joining in cisf i had intimated that i had given drdo examination before joining which by rule enables me for technical resignation from their . after that i got joining letter from xyz lab of drdo, i gave technical resignation in my old department and joined here .. submitted the copy of releiving order my servicebook and all other documents are also sended by cisf to this lab through office mode my do pt-2 is also done in which it is mentioned that i have been relieved from my previous job ....... sir .. my question is whether they can remove me now from job or later saying that u joined cisf after selection in drdo.. what is a candidate situtation in such cases where he joins somewher else even after selection and later wants to do that job again...... what is my legal position if they deny at anytime in future raising this issue .. as i have already given technical resignation in my previous department then if this department refuses me at any time in future i will be finished and loss my both jobs .. i m really confused with this