Trading of plastic granules

Dear all, we are auto seat manufacture and register in excise as a auto part manufacture. we are required plastic seat base which is we purchase from vender . we purchase plastic granules from market and sale to vender. when we purchase plastic granules we taken cenvate of excise duty and when we sale we charge excise duty from vender and paid to govt.but we do not have any licence of trading of plastic granules. the excise officer telling that you have not licence of trading so you have to reverse cenvat cedit. please suggest what can we do. Thanks