Product: Student loan

I'm reaching out because my wife and I don't know who else to ask for help. We're also reaching out to other state and federal representatives in hopes to get some help. In the fall of XXXX we completed a cash out refinance of our home in order to pay off my XXXX student loan balance. Our lawyer sent the check to XXXX  XXXX XXXX ( at the time Great Lakes ) who then cashed our check but didn't apply it to the account. After checking the account, it no longer appeared so we assumed the loan was paid off and the account was closed. Fast forward about a year later ( Fall XXXX ), we received a bill from " Nelnet '' with a $ XXXX loan balance asking for us to start paying on a balance which we thought was already closed. After over EIGHT months of disputing with Nelnet, they say there's " nothing they can do '' because XXXX XXXX has been dissolved. They both have a copy of our check ( which was cashed ) and yet they can not clear our account because they can not locate the funds through the XXXX XXXX provider who now no longer exists. This stressful situation has caused A GREAT DEAL of stress for our young family and we don't know who to contact to get it resolved since they keep sending us back and forth with no resolution. This issue has been " escalated '' within the upper management of Nelnet 's accounting department and they can see our verified documentation that the loan was paid and yet Great Lakes still sold our paid for loan to them anyways even after cashing it as if that wasnt the case. How can this happen and yet come back on the customer who has done their due diligence? Both entities have proof of payment and they took our money VERY easily and yet this mistake on their part is hurting us and our credit which weve worked very hard over the years to earn a good score. We always try to do the right thing and play by the rules but it seems without fail, we end up getting the short end of the stick because we're the " little guys. We were assured by Nelnet this won't affect our credit and, low and behold, it has multiple times, making it hard to qualify for financing for a variety of things we've been planning for for years. 
Considering the government didn't have my back when I returned from XXXX XXXX to help me acclimate back to society after serving in XXXX in XXXX, I accrued this debt as a result of my instability and poor judgment and shouldn't have. BUT, my loyal wife and I have taken EVERY step necessary since then to work hard and make the right choices for my family to get ahead regardless of those past reckless financial decisions. It seems I've been let down by my government now twice. PLEASE help us! Who do we contact to get this financial mistake resolved considering the Dept. of Ed is now gone. What an utter let down! I know the media would have a hay day with this story if they heard how the federal government has once again screwed over someone whos sacrificed for our country. We're ready to hire an attorney, more money out of our pockets we need to pay our mortgage, groceries and gas but well do what we have to in order for this to be made right. 
Thank you for your consideration in this disappointing matter. 
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