Business ProfileforQualia Collection Services

I got a letter saying I am being sent to collections for money I do not contractually owe. I lived at ********************* in 2020, my lease clearly stated ********************************************* ONE of two ways: certified mail or hand delivery with written receipt. These two ways were impossible due to lockdowns from COVID at the rental office, so I gave my move out notice by phone 4 months before move out. Before move out a property manager there confirmed that they had found the notice placed in my file and fixed the charges. I have sent them proof that the methods of delivery stated in the lease were unfeasible at the time and evidence that the manager found my notice before losing it again.I have paid all contractual obligations to ********************* and I do not owe them a "insufficient notice" fee as I provided more than the required 60 day notice by the lease Despite sending all the evidence, QCS have responded with a generic response stating they completed an "investigation" and determined the bill is due. They have not told me what would be required for me to prove that debt is not owed. I've sent returned certified mail, emails from managers and more to them Also, I've requested the current owner of this alleged "debt" and they have not told me whether its the property management company or them. Also they never sent me the signed lease