garage takeover

[VanSchaak]

I rent apt. and garage I converted into small recording studio with landlord permission.I've had studio 12 yrs.New tenate moves into apt on the property(musician) . I go to Sweden 2 months,give him keys to studio to practice.I come back home to find that he has dismantled, cleaned, and thrown out my gear, and set up his own gear claiming, he pays rent on the property, so he is entitled to access to the studio I've had for 12 yrs. I suspect he has has been slandering me to landlord to get me kicked out so he can takeover studio. What can I do?