If they are arguing that a lease becomes invalid if the premises are sold, they are wrong. Your lease runs with the premises. If they want you out early, they either need to find a basis to evict you for cause, or they need to offer you enough money (or other incentive) that you choose to leave early.
If they are arguing that they purchased the premises in May, and the person who supposedly renewed the lease the following month was not their agent and had no authority to renew the lease, that's another issue. How did you sign a lease with the former owners in June if they sold the property in May?

