Zero Balance Letter

Verizon has been TERRIBLE to work with. I cancelled my services with them and new I’d have to pay a small portion of the phones installments. However, the same month I cancelled I started being billed for a multi mobile protection plan for over $30 a month. They continued to charge this for several months AFTER the phones had been completely transferred to another provider. I started to receive bills to for the charges that racked up and called multiple time to resolve! I would get the run and around and even be told that someone would call back to resolve the issue. All with the verbals stating that a portion of the bill was absolutely inaccurate. I then started to receive a call to collect and that I only had a very short time to resolve or I’d have it reported on the credit. I gave verbal authorization, card number, and was told everything would be squared away. I never heard anything from that point on about an outstanding balance. I assumed they did what they was supposed to and made sure they payment I gave authorize for reflected. Fast forward about two months later I get another bill from Verizon stating I owe a balance I call and ask what happened and was told they no longer have the account and it has been sent to collections and is now reported on my credit. I was infuriated!!! I called to request records and have supervisors to listen to the call I gave permission to process such payment. I got the run around for over a month with promises that I’d get a call back the following day. I kept having to call, no one reached out to me.  I decided to just go ahead and pay the balance IN FULL again! They now will not provide a zero balance letter to me. They provided a very vague letter that stated debt had been paid. No date, no amount, and no one can provide any additional assistance. How hard is it for me to get a ZERO BALANCE LETTER with a date, first/last name, and account number?