Imo, the only reason to deal with Navient still is to gather information we talked about such as the bills, correspondence, communication logs, etc. It took me several tries to get each of these from my servicer. Each time it pretty much took getting transferred to and talking with a specialist. I got the best results by fax or mail (one request at a time), because they had to reply in writing. I understand why you had to talk with the advocate. Don't let them frustrate you because I doubt they were ever going to intentionally help. What they did do is show that they are unwilling to help and continue to lie. When you have these conversations, get the person's name, employee number and a summary of the conversation. I think every little bit helps even if they are just doubling down on trying to make this not their fault.
That's great if the Ombudsman can help you. If not, I got an excellent response from the CFPB complaint though. I haven't done one since they were reduced in enforcement ability, but I think they still produce results. Unlike some other complaint methods, you can submit multiple complaints. So if you had one successful complaint to get then to acknowledge/ fix the error, if needed you could do another to have them update the CRAs. I've also heard talk about people going to the Attorney General. I'm not sure if this complaint helps or not.
If the CRAs don't do anything, it wouldn't be a surprise. Since Navient is the source of the original problem and they refuse to admit it right now, so it seems everyone else is just acting on bad information, including the collection agency. There is another thread on here mentioning a lawsuit against another servicer. They said they had a similar problem and in the end had to get a correction when the CRAs. It took them years so maybe they have some information and tips that can speed along your process.
Good luck and hope you are able to find a legal remedy.