About relieving order

I recently resigned from my previous private company , they also collected the amount for my short notice period However my new Company which is A Government one wants relieving order, nut my previous company giving me only the work certificate. I have my resignation mail and the Full N Final settlement doc , So how should I proceed to get the relieving order. The previous company is also not ready to give NoC, In my resignation mail I requested both the documents but still they are not listening. Please help