Product: Student loan

My loans are with Nelnet and have been for a few years. I have always been in good standing for 12 years to be exact due to the fact I qualify for the Income driven repayment plan ; that I recertify for every year. My next recertification was due in XX/XX/XXXX. XXXX XXXX I received a notification of delinquent status for XX/XX/XXXX and XX/XX/XXXX from my credit wise account and XXXX points was deducted from my XXXX XXXX from Sloan servicing. I immediately look them up and contact them to see what's going on, and dispute the XXXX deduction from my score. The representative advised that XXXX is the sister company of Nelnet and some of my loans were transferred with them including the Income driven repayment plan. The representative also stated that they will review the credit report dispute and have contacted me via email on several occasions and by mail. Also, an XXXX XXXX application is needed at this time to stop the ongoing delinquency. However, the only mail I got from XXXX is the recent credit report review that they denied. I did a search through my email for XXXX and nothing comes up. I only have email from Nelnet. If I did get anything I would have handled whatever was needed immediately because I like to be in good standing with my accounts and have always been. During my call with XXXX, I recertified online while on the phone with the representative and the representative said it was received. A representative at XXXX told me that my Income Driven Plan recertification app was approved. However, I have not received any communication/mail stating it was approved or not. I asked the representative, if my loans and Income driven repayment app was transferred over then why would I be put in delinquent status when it was not due for recertification until XX/XX/XXXX. The representative just kept repeating, we looked into it and the account has been delinquent since XX/XX/XXXX and there is nothing they can do. I work very hard to keep a positive credit record. I never received anything from them, not a call, an email or, mail but a credit dispute review denial letter. Additionally, If I was delinquent since XX/XX/XXXX I would have been in delinquent status way before XX/XX/XXXX as their website states Until an account reaches 90 days past due, it's reported as up to date. When an account reaches 90 days past due, it's reported as delinquent. 
I repeatedly advised them I am not receiving any communications from them and to please investigate the communications issue further, through my BBB dispute. As of today XX/XX/XXXX I still have not received any mail from them. They clearly are not trying to fix the communication issue that will cause me to go in delinquent status in the future. Sloan servicing put me in a payment status when I already had and IDR app filed for XXXX and have damaged my credit by putting me in delinquent. I found that they have put several borrowers back in repayment without properly notifying them causing them to be past due and/or delinquent. I still have not received any communication from them, even after completing another XXXX app XX/XX/XXXX. I do not know what else to do to resolve this communications issue because they clearly do not care.