Product: Student loan

On XX/XX/XXXX Firstmark Services applied a credit to my account for the amount of {$10000.00}. This made XXXX of my loans be paid in full. 
On my statement of XX/XX/XXXX, I was not charged for this loan and the loan was removed from the statement. 
On XX/XX/XXXX I received a letter stating the loan was paid in full, they verified my information and notified the consumer reporting agencies. 
On XX/XX/XXXX I received another statement with no information on the loan that was stated to be paid in full and amount past due was {$0.00}. 
On XX/XX/XXXX I received a letter stating I was 24 days past due on the account for XXXX. 
On XX/XX/XXXX they removed an extra {$93.00} from my bank account over the amount showed on my statement. 
On XX/XX/XXXX I received a statement with the loan put back on a past due amount of {$93.00} and a payment due of {$93.00} on XX/XX/XXXX. 
On XX/XX/XXXX I received a letter stating I was 12 days past due for {$93.00} On XX/XX/XXXX I received a letter stating I was XXXX past due for {$93.00}. They also subtracted {$93.00} from my bank account on the same day. 
On XX/XX/XXXX I reached on to them about how my account. They informed me that I am past due by {$93.00}, they apparently had made an error and made in incorrect payment on my account. I asked for statements showing the error, how they fixed it and correspondence to correct me not being late on payments due to not being notified of the error when they tried to correct it, retroactively applying back the loan and not being late on any statement payments. They said they would get back with me. This took about an hour on the phone to get to this point. 
On XX/XX/XXXX I received a letter stating I was 10 days past due for {$93.00}. I reached back out to them since this is the first thing I have received since reaching out to them. They informed me I was past due on my account. Had to explain the entire situation again due to them having no notes about it except they had made an error. Was informed again they would reach back out to me. 
On XX/XX/XXXX I received a statement stating I was {$93.00} past due on the account. 
On XX/XX/XXXX I reached out to them multiple times to try to correct this error. After multiple calls I was informed that management had reviewed the account and that I owed {$93.00}. No letter, no correspondence, no corrected statements, no reasoning for the error nothing. Just that I had to take it for their word. I did not accept this as I have no statements with correct amounts or any information on how they made an error or corrected it. Was told they would get back with me again and would not correct or figure out the situation with me on the phone and that I would need to wait XXXX business days. 

After trying to fix this multiple times and getting no where. I feel that this could affect multiple things, like credit report, interests being applied to the loan, higher rates later when I consolidate due to multiple late payments. All this after already taking multiple hours out of my time to try correct an error they made. Also was never contacted by them to inform me of this error once they noticed it and tried to retroactively apply the loan making me " past due '' for a statement I never received. I have also received over XXXX calls from the company with no left messages but when I do answer it is just to inform me I'm past due but not correct the actual issue at hand. 

This has also affected another loan I have with them due to them applying an inaccurate credit to the account too and them performing reamortization on the account after applying this credit but then taking back out the credit. So now I'm not paying the correct amount on that account but they won't change it now.