You should not have to do anything if the leasing office has "torn up" the original notice since that would have been the proof of the basis for termination of the lease and then eviction (legally called "forcible entry and detainer"). If you would like to be extra safe, you could ask for a short note from the leasing office on their letterhead saying that the notice dated ____ has been withdrawn. If you want to write that note yourself, that is really what you need to focus on - identifying by date the notice that was issued and that it has been withdrawn accompanied by a signature from someone with authority to sign from the leasing office.
No need. It's not a court document.
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