The department's action of dismissing from service based on the outcome of the CBI court case judgement's confirmation wile the SLP was dismissed, appears to be appropriate to the rules of CCS (CCA) and invoking section 19 also proper. Your claim of double punishment to the same offence is not justified, however since you have approached the higher authority of your department, you may either wait for their action/reply or may approach CAT as desired, but the case is very weak on your side, so better take the advise of an expert service law practicing advocate in local by producing all the relevant papers/documents to him/her in person for possibilities if any in your favor.