Product: Debt collection

I resided at The XXXX XXXX, XXXX XXXX XXXX, Unit XXXX, XXXX XXXX, NV XXXX, from XXXX XXXX XXXX XXXX. Originally in a one-bedroom apartment # XXXX, until XXXX of XXXX where the rent was approximately {$900.00} a month, I coordinated with the apartment management to move into a two-bedroom apartment # XXXX where the rent was approximately {$1100.00}. 
Prior to XXXX XXXX XXXX, I made initial payments by cashiers check, which, included apartment deposits more than {$800.00} on top of the first months rent for the new apartment. Within a couple of weeks of living there, I was notified that my company was relocating me to Connecticut ( CT ) and I would have to be there by the end of XXXX. The same day, I visited the management office and notified the apartment management of this new relocation development. They informed me there is a 60-day minimum notice exit from the lease, which, meant, from the date I, first notified them, approximately XXXX XXXX XXXX, I was obligated to pay rent for 60-days or two months ( approximately XXXX XXXX XXXX ). I was told with my discussion with the manager that I would not be able to pay XXXX 's rent using their online payment system, since I would be removed from it, but, the agreement was to cover up to mid-XXXX ( my 60-days ), they would keep my deposit from XXXX of {$800.00} and bill/refund any  difference, based on the rent, should have been approximately {$600.00} or less. 
XXXX 's rent was paid prior to my move in and I paid XXXX 's rent via their online payment process, as required, and departed the area on XXXX XXXX XXXX for Connecticut. Prior to my move, I rented a USPS post office box in XXXX, CT ( she and my daughter were there to enroll my daughter in school ) and submitted an official changed my address with USPS for my XXXX XXXX mail to begin being forwarded ( the email stated it would take two weeks ). I called the apartment management office and provided my new mailing address. All my possessions were professionally packed and moved out. I cleaned the apartment and turned in all keys and remotes ( to  garage ) on XXXX XXXX XXXX, where I moved to a hotel near the airport in XXXX XXXX for my remaining couple of days. 
At no point from the end of XXXX XXXX to XXXX of XXXX did I receive any letters, emails, or phone calls. Approximately, midXXXX XXXX, I received a call from what is now Sentry Recovery, a collection agent, attempting to collect {$700.00} for money owed to my former apartment in XXXX XXXX. I immediately called them and spoke to XXXX who, after a few minutes of " research '', tried to tell me they had tried to contact me and they had left voicemails on my phone. I explained to her it was impossible, as my phone was the same number and NOWHERE in the history or voicemails were there any messages from the complex. She told me there was nothing she could do, since they had referred it to a collection agent. I asked her to send me a copy of any bill or invoice so, I could examine it. She refused and referred me to the collection agency. I called the collection agency back, the same day, and made a good faith payment of {$100.00}, but, told them I needed confirmation of this debt and would not pay anymore until I had it, they were, evidently, just getting started and did not have email or a way to send me a receipt for my {$100.00} payment, so, I requested it be mailed to me, and I provided him my now home address in XXXX To date, I have never received confirmation of this debt or a receipt for my payment. I have disputed this with the credit agencies and it should be reflected on my credit reports accordingly. 
As mentioned in the spreadsheet, I have challenged the validity of this debt and also sent a similar statement to the 3 major credit reporting agencies.