Product: Student loan

My daughter has a private student loan with XXXX XXXX XXXX. I am the cosigner and we elected the monthly interest only payment plan while she is still attending school. In XX/XX/2020 when my daughter was sent home from school due to Covid-19 she was unable to work. We decided to file for the Covid-19 deferment of her student loan payments for 3 months. In XX/XX/2020 we began receiving correspondence from XXXX XXXX  about her deferment period being up on XX/XX/2020 and her loans would go back into repayment. The repayment details reflected an amount that was not just interest only, it also reflected a repayment amount as if she was in total loan repayment status. When I contacted Firstmark ( the company that serves the XXXX XXXX  loan ) about this error I was told that this is " new '' and that they were trying to figure things out and asked if I could be patient. I was assured that in XXXX, we would begin a repayment amount that reflected interest only. I was understanding and agreed to be patient while they worked out the kinks. In XX/XX/2020 we received our first repayment bill due in XXXX. It was a very high amount and did not reflect the interest only. I called to have this corrected and paid the interest only that was owed. I was assured that this was being worked on and would be resolved by the next billing statement. In XX/XX/2020, again the bill was wrong and did not reflect the correct amount. I requested to speak to a supervisor. After going back and forth, the supervisor was able to see the error and adjusted my account. I was again assured that this issues would be corrected as they submitted an expedited request. This cycle of receiving incorrect bill repeated monthly and still continues today. I have been reassured on numerous occasitions that the issue would be corrected and expedited. I have been told that I can not speak to anyone above a supervisor, I have also been told that supervisors have not done their jobs by other supervisors. I was assured that we would not be sent to collections. In XXXX XXXX, my daughter received her first call from XXXX XXXX  collections department. After she received this call, I contacted XXXX who indicated that no one called her as they had no record of her account being delinquent. This meant that the issue had been resolved and there was nothing they could do to assist me, On XX/XX/2020 my daughter received her second collections call from XXXX. This call resulted in them making her repeat a promisary statement about repaying her delinquent funds to Firstmark. My daughter was 200 miles away at school and has severe XXXX. Due to this, I contacted Firstmark again, and was told that they were fixing my account, however, there was nothing they could do to stop the calls and that we needed to deal with it. As of today, I am receiving bills with incorrect repayment amounts, as well as late charges for funds that we are not late on. In fact, we have not missed any payments, other than the 3 payments while the loan was in Covid 19 deferment. I was informed that this would be added to the end of her loan repayment schedule, which would extend her loan by 3 monthly payments to equal the 3 monthly payments that were deferred. This experience has affected both my daughters and my own mental health.