Complaint sub-issue: Trouble with how payments are handled

My consolidated federal student loans ( originating XX/XX/XXXX, University XXXX ) were transferred to Nelnet in XXXX XXXX. I began payment on them XXXX XXXX, with no late payments to date. At 36 months ( XXXX XXXX ) of on-time payments, I am eligible for -1 % to my annual interest rate. My monthly loan payments were paid by auto-debit via the Nelnet internet portal. I was signed up for e-correspondence via email including alerts. On XXXX XXXX, I noted that my account had not debited and contacted Nelnet. They informed me my auto-debit had been canceled because the bank " told [ them ] my account was closed. '' I asked about my incentive and they said I had been disqualified. I asked how I could reinstate my incentive and they stated to get a verification letter from my bank stating the account is open. I asked to speak to a supervisor and was transferred to a Resolution Specialist ( XXXX XXXX ). He submitted a " research request '' to " look into it '' but would not answer repeated requests for information about documentation. He stated it was probably Nelnet 's error but was not sure how to prove this, and stated he needed proof of this to reinstate my benefit ( and would not further clarify this circular reasoning ). I called my bank ( XXXX XXXX ) ; they stated the last payment request from Nelnet was on XXXX/XXXX/XXXX ( which was paid XX/XX/XXXX, see attached screenshot ) ; they did not receive a payment request for XX/XX/XXXX. ( My bank account has been open and has had no period of insufficient funds, see available balance on screenshot ). The bank issued a verification letter as requested. I also called Nelnet back, with a XXXX XXXX online banker on the line to provide verbal verification of no XX/XX/XXXX payment requested, to verify my open account with no recent changes. XXXX XXXX was unavailable, and the Nelnet account representative refused to document the verbal verification stating it would not help my case. 
I have at no time received notification from my bank of a stopped/refused payment ( which XXXX XXXX states would happen if a payment was requested and refused ), nor email from Nelnet stating payment was refused, despite signing up for alerts and email correspondence. There is a message posted to the Nelnet borrower portal inbox ( but not emailed to me ) stating refusal of payment and cancellation of auto-debit dated XXXX XXXX, XXXX - but this was not emailed, and it was dated after the late payment due date. I had no way of rectifying the situation in time to submit an on-time payment. The bank has verified that Nelnet did not submit ANY request for the XX/XX/XXXX payment ; moreover, my account was open with routing/account numbers unchanged and correct. 
1. I am concerned at the suspicious timing of this " error '' : at month 34 of on-time payments, just prior to the initiation of my -1 % benefit. 
2. I can not receive a clear answer from Nelnet as to how to determine what the error was. 
3. The bank states no payment request was made for XX/XX/XXXX ; all prior payments were successful and no banking information has changed since XXXX XXXX, when it was updated in Nelnet 's online borrower portal. 
4. I was not notified of the payment refusal by email despite being signed up for email correspondence and alerts. 
This " error '' will cost me ( and profit Nelnet ) ~ $ XXXX over the expected life of the loan. 
Thank you for your consideration of my claim. I request reinstatement of my -1 % to APR benefit to begin XXXX XXXX as planned.