From the facts stated, it seems the landlord did breach the terms of the lease by failing to give proper notice. However I doubt that any court would allow a single breach to allow terminating the lease. Give written notice to the landlord of your complaint and wait for a second incident.
Write a letter stating that you require specific notice at least 24 hours in advance of the date and time of any non-emergency visit. State exactly what happened and that this is an invasion of privacy. Point out that, while it my not have been intended by management, some employees may use this as an opportunity to surprise tenants, especially women, who are not fully clothed in the privacy of their own home. Tell the landlord that you will call the police and consider it a breach of the lease if it happens again.
Clifford L Tuttle, Jr.
Attorney at Law