Illegal possession

Hello sir, I purchased a land on 2012 with unregistered document. one person who introduced with my friend took my documents saying that he will get approval for house construction. by believing him i gave the documents. last month i went to see my land i shocked that one person has occupied the land and also he made simple shed and living there. When i asked him he shown a registered power document. I have surprised that power document shown that i gave a power to him, he misused my signature, and also i dont how it was allowed by registrar office. As per on of my friends advise immediately I cancelled the power document, later only realised that since i am not given the power, it's not advisible to cancel the power by myself Immediately i called police, and gave complaint against the tresspasser. but there is no use, the person influenced the police, and the police said it's a civil issue, you go to court for remedy. Please guide me what is the case i have to file against him ? Is there i have to pay heavy court fee for the suit ? How can i prove that the power is not given by me ? What is the further procedure i have to follow ? Thank you