Renters Rights Legal Advice

Houston Apartment trying to hit us with a broken lease for “turning end of lease (30 day) notice in too early”. I’ve never had an apartment say that we couldn’t turn one in earlier than. As long as it’s prior to the 30 days required shouldn’t it be accepted? We finished out our lease and even turned in our keys on our actual move out date. Lease ended June 30th we turned it in mid-March.