If you have a landlord, then it is not "your" basement. You are renting, right? If the use of the basement was not included in your lease, he had every right to remove anything that he felt was a fire hazard, or any stuff he didn't want there, for any reason. If you wanted to store stuff down there, you should have asked. It's likely at the dump - you can't get it back.
Certified Paralegal, with 25+ years' experience & with Landlord & Tenant law experience.