Product: Student loan

I consolidated my school loan in XX/XX/XXXX when someone from XXXX reached out to me and told me it would be wise because interest rates were rising. Unaware of what I was doing or what it was, I did in order to lock in my interest rates. I was told I could receive a XXXX % interest rate reduction if I had autonatic payment withdraws and after XXXX on time payments I would receive an additional XXXX   % interest rate reduction. 
My loan was sold and/or serviced by three different companies since the consolidation ( XXXX, XXXX, Nelnet ) I was in forbearance or deferment until XXXX ( when I began stable employment ). I forgot all about the incentive programs. I made consistent on time payments starting XX/XX/XXXX, at which time XXXX withdrew the monthly amount from my checking account. In XXXX or early XX/XX/XXXX, I was informed effective XX/XX/XXXX, I would have a new servicer ( Nelnet ) and they would be responsible for my loan ( they assured me all information would be transferred over, if I had automatic payments it would continue as agreed with XXXX ). In XX/XX/XXXX, my interest rate was reduced by XXXX  % ( at that time, I remembered the statement about XXXX on time payments ). In XX/XX/XXXX, Nelnet raised my interest rate back to what it was previously, stating I did not qualify for the incentive. I begin calling Nelnet multiple times to figure out what the problem was. A Nelnet representative informed me I did not qualify for the incentive because I had missed a payment. I asked when, seeing that Nelnet had been taking money out of my account on the XXXX of every month. The Nelnet representative stated the information they received disqualifying me was from when my loan was with XXXX and I needed to contact them for more information. After reaching out to a XXXX representative she was unable to tell me when I was disqualified or when I missed a payment and started working with me to work with Nelnet. Finally after a month and a half, I was informed that I was disqualified from the XXXX % interest rate reduction incentive in XX/XX/XXXX. 
My question to Nelnet, how can I be disqualified from the XXXX % interest rate reduction incentive prior to even making payments?

All of this happened because Nelnet gave me the XXXX % rate reduction for 5 months, took it away and adjusted my account accordingly. At the time Nelnet had offered the XXXX  % interest rate reduction, I had already made 72 months of on time payments ( 36 months auto withdraw with XXXX, 36 months auto withdraw with Nelnet ). Technically, my interest rate should have been lowered by XXXX % effective XX/XX/XXXX, 36 months after I made on time consistent payments to XXXX, and then the terms should have remained once Nelnet became the new servicer. 
I feel Nelnet is not honoring the agreement I had with XXXX when I consolidated in XXXX. I made 36 on time consistent payment as of XX/XX/XXXX, at which time my interest rate should have dropped by XXXX %. 
I have since paid the loan off because I did not like the treatment I received regarding this matter. I feel Nelnet should have to backdate my account to XX/XX/XXXX and make my interest rate reflect a XXXX % lower interest rate and refund me the over payment.