Commercial Building's Illegal possession

We have a commercial building which was rented out in the early 90's. There was no agreement for this property. Also, there is no other paper work on that building. Now, we want our building back from tenant but he says that he will not give it back to us and he has Kabja on the building. We are not sure what will be the appropriate ruite to handle this situation. Please suggest us a fool proof and short solution.