Product: Debt collection

National Credit Systems is listed on my credit report as being a joint collection account, for an apartment complex with a balance of {$4400.00}. This is not my account, it is my mothers as she lived there, and we have very similar names my name is XXXX XXXX XXXX and hers is XXXX XXXX XXXX ( XXXX ). She used XXXX and XXXX as her last names separately and in combination of both at times because her professional degrees and certifications were listed in XXXX XXXX, so she kept that last name even after her and my dad divorced.. 
My mother is the only person who was on the actual lease as she lived there. However, she was being treated at XXXX XXXX for XXXX XXXX XXXX so her health was dwindling and I needed to be there with her so I could handle all the things she was beginning not to be able to do anymore. It was approximately during the last 2 months of her lease.. These included keys to apartment, keys to mailbox, maintenance requests, and so forth. In order for me to obtain these items, the staff at the apartment office said they needed to add me to the lease as being an occupant in order to authorize and grant permission as well as made a copy of drivers license.. Unfortunately, she unexpectedly passed away XX/XX/XXXX. 
National Credit Systems ( NCS ) has placed this account on my credit reports as they claim I was on the lease, which is incorrect. Whether it was the apartment complex that confused the paperwork or whether it was NCS not having all of the documentation necessary to prove this account is being reported accurately. My most recent dispute was on XXXX with XXXX explaining that this account is not mine and I gave the same details as I have included in this complaint. Shortly thereafter, the dispute had been completed and XXXX stated that this account was verified as being accurate from NCS. On XXXX, I sent a debt validation letter to NCS, including providing me with any and all documents that were used in their investigation. This was completely ignored. I received nothing from NCS. 
Today, XX/XX/XXXX, I called NCS to inquire about this account as I had not received any type of response to letter dated XXXX and it caused me to be denied to purchase my first home. I spoke with a XXXX XXXX, who refused to repeat her first name to me, and then proceeded to say : XXXX ) This debt wont be removed by disputing it XXXX ) Told me I was the one who needed to show proof to them that this account was not mine and to prove to them the inaccuracies in the account being reported. 
XXXX ) Upon me mentioning the debt validation letter I sent to them on XXXX that was ignored, She stated that they are not required to send me all the documents and information they have in their file, regardless of whether or not I requested it. 
XXXX ) XXXX XXXX continued to mix of my words into what she wanted attempting to catch me as she assumed and began to make personal derogatory comments about there being no way that my mom was able to pay all the bills on her own, without a job, and failing health. This was unprofessional, and she has no idea about my family and its financials to make such a bold statement. 
XXXX XXXX proceeded to re-iterate this debt would not be removed by disputing, whatever she meant by that. This account needs to be removed from my credit file and release any liability that NCS alleges I have for this account. I have attached the Debt Validation letter I sent to NCS on XXXX that they blatantly ignored. Since this account was also illegally re-aged by NCS as they changed the date of last activity from XX/XX/XXXX to XX/XX/XXXX. I have attached a screenshot of that as well. Both of the listed dates for date of last activity that NCS claims to be accurate, are inaccurate. this needs to be handled asap as this account has been inaccurately reporting to my credit for far too long when it is not mine.