plz help special relief act

The son has not recognized you as owner.

You may show the registered sale deed and mutation record and notice received by you from son to a local lawyer handling property/revenue cases and contest the matter. 

Though the son of previous owner of land knew it very well that questioned land is in your possession and mutation record also in your name but he wants to get declaration from court  that he is owner of land so you have to contest the case on the basis of sale deed and mutation order.