Product: Debt collection

I am a co-borrower on a mortgage with my son. In XX/XX/XXXX our lender changed processing systems. Prior to the change, we were signed up for and received payment due and past due text notifications, and all payments were made on time. After the system change, the XXXX and XXXX XXXX payments were not made and neither of us were notified. My son activated auto pay in XX/XX/XXXX and the lender said they had no record of it. They asked for the auto payment ( done immediately prior to the conversion ) email we received for evidence, indicating we should have saved it. How would we know to save an email? We both pay all of our bills that allow online payments electronically, and never had any issues. I also asked the lender why I did not receive one phone call or correspondence that a loan I am co-borrower on was delinquent. She stated they only communicate with one borrower and have no obligation to me as a coborrower. However, they reported this loan to the credit bureau, and my credit rating dropped XXXX points in one month.

The customer service agent stated a nonpayment letter was sent to my son on XX/XX/XXXX, however it was sent to the wrong address. No such letter was sent to me as the co borrower. The lender 's portal includes a document and correspondence section, of which no such letters of nonpayment were included. Looking through the addresses on the documents in the portal, illustrated different correspondences were sent to different addresses of my son and no correspondences or phone calls were sent or made to me, even after XXXX payments were not received. The lender sent nonpayment notification letter to the property address, which is not where my son or myself reside, which was also noted on the closing documents ( done in XX/XX/XXXX ). My son relied on the auto payment, like he does for all of his bills, and checks payments every few months. This experience has surely changed that. 
In XXXX, when my son realized the loan was not paid for the month, he tried to call to address it. I also tried to call the lender and we both aways experienced significantly long wait times and being transferred to several areas. I finally reached an agent on XX/XX/XXXX and I requested a credit report claim after explaining the sequence of events above and lack of corresponded with us, as was told I would receive the form in XXXX business days. I was also told that once I completed the form, I would then return it to the lender and they would process it and determine next steps. I did not receive the claim. I called numerous times in between daily work meetings and finally spoke with an agent again on XX/XX/XXXX inquiring about the status of claim form. The agent gave me a customer complaint number to call ( XXXX ) to inquire why again a correspondence ( credit claim ) I should have received was not sent. The phone number is a voicemail asking for my information and stating my call would be returned. 
I am a XXXX  and work in a financial institution and value my credit rating. I don't feel this borrower communicated with us, and had system errors when implementing their new payment system, that was the cause of this significant impact to our otherwise strong credit. We feel like we constantly go in circles with no resolution, and now have a low credit score that we worked diligently to maintain over our lifetimes, and the lender has provided no support in this matter. If this was a mistake, even after this frustrating experience, we get it, and just want it fixed.