Is a lease non renewal for lease form a legal document.

We were given a Non renewal form at the end of our lease. It was on a company leaderhead, and signed by our property manager. It stated out deposit, as well as money will be taken out for repairs, damages, and due rent. With this language my family and I started moving to a new home, expecting the deposit (which is about $600 more than rent) to cover our monetary obligation to the management company per the Non-renewal. We did not pay the rent thinking that the (per the notice) deposit would cover the rent and we could use that rent to put down a deposit on the new residence, which we did. Now the company is stating that the non-renewal is not a "legal document" and will not stand up in court, and are now wanting to evict us even though we are moving in less than 7 days. Is the lease non-renewal form a legal document, it was on company leaderhead and signed in ink by the property management.