Complaint sub-issue: Trouble with how payments are handled

I went to XXXX XXXX between XXXX and XXXX and, in addition to federal loans, I took out XXXX Sallie Mae Smart Loans through Sallie Mae, which was advertised to me by XXXX XXXX in my XXXX as a good student loan provider. 
Between XXXX and XXXX I took out XXXX loans with the company. I have been out of school for 6 months and I pay them every month on or a few days before the day that they are due. 
We had a problem in XXXX with XXXX loan amount not going through. We were not notified until a letter came in the mail in XXXX saying I had a loan that was over 15 days past due. When I called the company and checked my loan statement, it showed that there had been a Payment Reversal on XXXX of my XXXX loans and a late fee had been charged to me. I called the Customer Service number. A Sallie Mae representative told me that the payment had been applied to the previous month by mistake ( despite that I had paid XXXX on time ). I asked them to remove the late fee that had been charged to me and she said that would not be a problem. 
Then on XXXX/XXXX/XXXX, I received an email from Sallie Mae saying only that my account required " Immediate Attention. '' I called the customer service line and logged into my account. The payment I made in XXXX had reversed, just like the XXXX in XXXX, and another late fee had been charged to me. My minimum payment for the loan had hiked up to {$75.00} to compensate for the months I had " missed '' and the reversed payments would now affect my father 's ( my co-signers ) credit score. 
I payed that loan and my other XXXX loans right then and there. The representative for that phone call said that the payments had reversed because the company had lost or could not find the account number. This did n't make sense. I pay with the same bank account for each loan and the other XXXX loans were fine. All the numbers registered to my account checked out on the computer. 
To make sure everything checked out, I logged into my Sallie Mae and my bank account on XXXX/XXXX/XXXX. My Sallie Mae account said that my loans had all been paid on time - including the loan that had reversed my payment XXXX. I checked my bank account statement. the account showed that XXXX loan payments had been charged to my account on XXXX/XXXX/XXXX but the XXXX loan had not yet been charged to me. I called the customer service line again. A different representative said that while he could not ( for some reason ) transfer me to my account manager, it looked like my account was up to date on payments and that my father 's credit score would not be affected since I had taken care of the problem before the XXXX day of delinquency. 
The problem of course is that my payment has reversed two months in a row with no adequate explanation or fix, meaning that the XXXX payment is now over 30 days delinquent. He said that while my bank account had not yet been charged, Sallie Mae had accepted all of my loan payments and that I should check back in a week. 
I went back and checked my previous Sallie Mae payments for that loan and found that through XXXX XXXX, my payments had been going well. Then in XXXX XXXX my payment reversed ( I was never notified or charged a late fee for that XXXX. I did not even know until I went back and checked the transaction history ). That is XXXX payments that have reversed with no explanation and little help. 
What is more frustrating is that I am not notified of the problem in enough time to take care of it. I am fully capable of paying on time, but not being able to is causing me unnecessary stress and future credit problems.