The Answer;
In the name of Allah, Most Gracious, Most Merciful.
Though you may have been granted a Civil Divorce and have a Decree Absolute, Islamically, you will need a valid certificate of divorce to anull your marriage, which is the exclusive right of a Qadhi. A Decree Absolute alone, does not constitute a Shari’ah divorce in Islamic law. Without undergoing this Shari’ah process, or the express three fold use of the word “Tilaq”, a woman will not be considered as divorced from her husband. It is advised for you to seek the advice of a qualified Qadhi in your locality to finalise your Islamic divorce, as per the Shari’ah.
And Allah(swt) alone knows best.