The first question is whether this is a lease with the apartment landlord or a sublease with a lessee of such landlord. The second question is whether the lease itself specifies a specific floor plan, square footage and, most importantly, unit number. These are very important facts to know in order to answer your question properly.
Tenant-landlord disputes can be quite complicated, and you should speak with an attorney to understand your rights, responsibilities and any claims you may have against the landlord. I handle many tenant-landlord matters in Delaware and would be happy to discuss this matter with you further.
DISCLAIMER: The above is for informational purposes and no attorney/client relationship is intended or implied. Such a relationship can only be established through the signing of a retention/fee agreement.