Got a “30 days to default” letter from Nelnet but I’ve been making payments – mistake?

Hey all, I just got a scary letter from Nelnet saying I’m delinquent and have 30 days to avoid default. The thing is, I’ve actually been making payments, so this honestly came out of nowhere. Payments have been coming out of my bank account, and I don’t recall missing anything. I also didn’t see any warning emails before this letter showed up. Auto-pay might be involved, but I’m not 100% sure yet.

Has anyone else dealt with something like this? I’m wondering if this is usually a servicer error or a case of misapplied payments. My plan is to check studentaid.gov, pull my full payment history, and call Nelnet to request a full payment audit. If you’ve been through this, what should I specifically ask for when I call? Is there anything I should avoid saying? And how likely is it that they actually fix it if I have proof? Any advice would be appreciated because this is stressful as hell.

https://imgur.com/a/RPBw3KX