How to gain possession of a property which i bought .

I have bought a house in Lucknow . It is a house of 1380 sq. feet. i have bought it through a sale deed in 2015. The owner of the property had given me the possession at that time. I had locked the property and do not went to it for 3 months . when after 3 months i went to my house. what i have seen is that the lock of my house was broken and some people are living in the house. All the items from my house are stolen. and they threaten me that if i again went there they will kill me .they are the same people living just beside my house and they were the relatives of the previous owner. i told this issue to the S.H.O of my area , he has told me to give an application so that they can register an FIR. so my question to all respected lawyers is that what should i write in my application so that i can prove my possession of the above property. They are saying that the above property has not been partitioned . then how it can be sold . what criminal proceeding can be done to them and how do i prove my possession of the property so that it can be under my possession again without filing a civil suit. also reply if filing a civil suit is necessary . i have got my name registered in the municipal corporation and got the tax receipt of house tax and water tax. Please reply .