Product: Student loan

( 1 ) XX/XX/XXXX - received a letter from my previous student loan holder ( XXXX XXXX XXXX/XXXX ) that they sold my loan to XXXX XXXX XXXX ( XXXX ) /XXXX XXXX XXXX XXXX . Tried to contact both for updated billing statement but XXXX " could not find me in the system anymore because of the transfer. While XXXX " could not find me because it 's a new account. '' ( 2 ) XX/XX/XXXX - received the first bill from XXXX already stating I owed more than what 's due because of a late payment from XXXX record ( which by the way, no one can find proof of, and my bank shows on-time ( not late ) payments sent by ebill. Usual due payment is {$170.00}, but I had to pay them {$190.00} for a late fee of {$20.00}. After so many back and forths with both companies who still could n't find me but was quick to tell me how much I owed, I paid the higher amount while they promise refund after due " investigation. '' ( 3 ) XX/XX/XXXX came with multiple bills from XXXX : - 1st statement : XX/XX/XXXX showed the correct due amount of {$170.00} with {$0.00} additional Fees Due. 
- 2nd statement : XX/XX/XXXX showed an on-time payment of said {$190.00} from the previous month ( XX/XX/XXXX ) and a due amount {$150.00}, but there 's an additional Due Fee of {$20.00}. Now, I 'm confused. 
- 3rd statement : XX/XX/XXXX showed same info as above XX/XX/XXXX - 4th statement : XX/XX/XXXX showed same info again as above XX/XX/XXXX. 
** all these statements have different tracking Document ID numbers ** ( 4 ) XX/XX/XXXX XXXX bill came with interesting charges : - statement XX/XX/XXXX showed an early receipt ( XX/XX/XXXX ) of last month 's payment of {$180.00} ( more than what 's due ) ; an added Due Fee of {$20.00} ; and a total due amount of {$240.00}!!! 
So, I paid early & more than what 's due from the previous month bill, and then I get hit with extra charges! 
- I called customer service who was struggling so much looking for me on file. He knows I owe, and have, late fees ( which he could n't explain why ), but he ca n't find anything else, or he has " no access to my information. '' After several more back and forths, and multiple requests to speak to someone else or his supervisor, he finds me in the system! He confirms they received my payment on-time as I confirmed with my bank, and states " it was an error in their system upgrade. '' Bids goodbye and gives a promise it wo n't happen again. 

( 5 ) XX/XX/XXXX bill was not improved. 
- statement XX/XX/XXXX showed early/on-time receipt of previous month 's payment of {$180.00} on XX/XX/XXXX. Showed {$0.00} Fees Due. But a Past Due Amount of {$84.00} and Total Due of {$260.00} - I call again. The same painful situation of " sorry ma'am, I cant find you in the system '' despite trying multiple personal data that should be on the record. She even went as far as asking me where I went to school? ( does not matter! ). After, yet again, another painful extended period of time on the phone, asking for the supervisor, she finds me! Confirms receipt of payments on time and apologizes for " upgrading system in error. '' She confirms due amount should only be {$170.00}. Supposedly corrects the problem, and this wo n't happen again. 

( 6 ) XX/XX/XXXX comes along with yet another wrong bill. 
- statement XX/XX/XXXX : shows on-time payment again with the amount paid more than what 's due ( XX/XX/XXXX, {$180.00} ). {$0.00} Additional Fees. Past Due Amount of {$81.00}. Total Due of {$250.00}! 
- Customer service briefly struggles to find in their system, and again uncertain what the extra charges were for. Speaks with her lead and tells me they are aware of the problem and cant do anything about it until XXXX XXXX XXXX XXXX tell them something. CSR continues to say XXXX is just the billing system. I cant even find a contact number for XXXX! So in the end, I was told again only to pay whats originally due ( {$170.00} ) and ignore other charges while XXXX XXXX XXXX investigates the matter. Meanwhile, these " past due charges '' are increasing by the month! 

As you can see, I pay on or before due dates of each month, and a little extra for principal payment ( {$180.00} instead of the due {$170.00} ). 

How many times must I call to correct this problem? How much stress and harassment must I endure to correct this problem while the supposed unexplained " past due charges '' increase? 

I am certain I am not the only one being billed erroneously. This can account for thousands, if not millions, of fraudulently collected money. Please help! Please advise. Thank you.