Complaint sub-issue: Trouble with how payments are being handled

Issue : Firstmark has not been applying my overpayments to the loans with the highest interest rate, but rather spreading the overage equally between my four loans. This is not correct. The overpayment should be applied to the loan with the highest interest rate, this I how my previous servicer allocated payments and this is how Firstmarks website advertises their overpayments will be allocated. I have requested this because about the same time that Firstmark took over my loan I went back to school for my XXXX ( in XXXX ) and was in deferment but was still making regular monthly payments. These payments were not being applied correctly and therefore have effected the amount of interest I am paying vs. principle. In addition, over the past year and a half I have been paying in excess of my regular monthly payment in order to try to get the loans paid off, and none of those excess payments were being allocated correctly either. 
Discovery : This was discovered in XXXX when I went to pay off one of my loans. It had a remaining balance of around {$930.00} and I made a payment of {$950.00}. After a couple of days I went online to check to make sure the loan was paid off and it wasnt because the overpayment was split up between my open loans. It is important to note that two of my loans have interest rates that are the same and are lower than the other two which have the same interest rate and are high. A few months prior to discovering this, one of the higher rated loans had been paid off and as a result of the {$950.00} payment allocation the 2nd loan with the high interest rate was also paid off. *this comes up later in the requests Request : I have made multiple phone calls and requests in order to get this resolved with Firstmark going back to XXXX. I was first told it would take 2 weeks to review. 4 weeks later I followed up with them via their online contact sheet on XXXX asking for an update. To which they replied that it was corrected. When I went online only the last {$950.00} payment was reallocated and not the whole history of payments like I had requested to them on the phone and in writing. I filled out another online contact form on XX/XX/XXXX explaining in more detail what was needed and again requested that all payments would be reviewed. I received a response that my request was received on XX/XX/XXXX and that the payment request was under review which would take XXXX weeks for processing. I then followed up via phone call on XXXX and the customer service rep told me that nothing was reallocated because the 2 loans with the highest interest rate have been paid off. I again explained my story and advised what I wanted to be done. The rep seemed like she understood, said she was going to talk to her supervisor, escalate the matter and have someone contact me within a couple of days. A few days went by, On XX/XX/XXXX I followed up with them again as I hadnt heard anything. They advised that nothing had been done. On XX/XX/XXXX I followed up again and was told again, that nothing had been done. I requested to speak to a supervisor, once again explained the situation and was told that she was going to personally pull my request and have it resolved. XX/XX/XXXX another phone call placed and was told that nothing has been done but it should only been a couple more days and that it was rush status. And today another request for update was made and nothing has been done.