Complaint sub-issue: Trouble with how payments are being handled

My husband 's student loan was sold to Great Lakes in XX/XX/XXXX. They stopped sending us paper bills and when we missed a payment, would then send us threatening notifications of our negligence. Once I received a paper bill ( after 2 requests for one ), I promptly paid it. A few days later, I received a threatening letter in the mail stating due to my negligence, my credit could potentially be harmed as I had not paid my bill. I promptly called on XX/XX/XXXX and spoke with XXXX who said my payment was processed, then returned. He was not able to tell me why the payment was accepted, processed, then rejected. He suspected the address of the payee was changed ( unknown to me ) recently and this may be causing the issue. XXXX said he would look into this further and would get back with me within 3-5 business days. 2 weeks later, I had not heard from him so I called Great Lakes again. This time ( XX/XX/XXXX ) I  spoke with a supervisor named XXXX. By this time I had received another bill, adding a {$9.00} late fee to my balance due. XXXX claimed that due to my error or my bank 's error, the payment was sent to an address in XXXX ( which she claimed was the DOE ). Here, she said the DOE attempted to figure out which loan vendor I was trying to pay but could not and sent the payment back. I questioned her as to why the payment would then show as initially credited on my husband 's account if they could not determine who I was trying to pay. I assured her I manually entered the address for payment as it appeared on my statement. I asked for a guarantee my payments would be properly credited moving forward and to reverse the late fee. She refused so I ended the call and contacted my bank, XXXX XXXX XXXX XXXX.  There, I spoke with a woman named XXXX who said there was never an XXXX address on my account and indicated the payment was made in a purely electronic manner, eliminating the need for a physical address. 
On XX/XX/XXXX, I spoke with my bank again, who assisted me in phoning Great Lakes. This time we spoke with XXXX, who identified himself as an account manager. After XXXX ( my banking representative ) described to him the error code, and electronic payment mode, he continued to argue with her and state it was mailed to a physical address in XXXX. He stated he was not sure why XXXX and XXXX responded the way they did on the initial calls. He stated he was going to " email them '' ( I am not sure who at this point ) to figure out the problem. Repeatedly, XXXX and I asked what we could do to make sure future payments would be processed correctly ( we double checked the account number and address, which XXXX said were correct ). XXXX was not able to tell us how to proceed. I asked XXXX to have this issue resolved, I would need to know my future payments would be credited properly and I would need the late fee reversed as this has been proven multiple times not to be my fault. He replied he can not do those things at this point and has guaranteed a call back today. I asked him his suggestion on next steps if he fails to call me back, like XXXX had and he again assured me he will call me back today. Regardless of the outcome I am certain I am not the only person who has had issues with fraudulent documentation by this company. I hope you are able to investigate them. I can be reached at XXXX and XXXX.