I obtained a car loan with Santander in XXXX. My overall problems with Santander did not begin until after I submitted a lump payment of {$13000.00} in XXXX XXXX. Since my monthly payment is {$350.00}, I paid my loan forward for XXXX years which I needed and wanted to do since I was/am unemployed and did not know when I would obtain adequate employment to make monthly payments. I received documentation from Santander stating that I paid down my loan to less than {$1600.00}. I did not make any subsequent payments after XXXX because I knew that I paid forward until late XXXX or even early XXXX. I received a statement from Santander in XXXX XXXX saying that I was late on my XXXX XXXX payment. I knew that this was impossible since I had paid XXXX months of payments in a lump sum in XXXX. I called Santander and listened to the voice prompt that assured me that I had paid {$13000.00} in XXXX because I was thinking that there was a mishap since I received a statement that I was late with a payment. I spoke to a representative who told me that I had made a payment of {$12000.00} in XXXX ; he placed me on hold when I disputed this amount and when I informed him that Santander 's system said that I made a payment of {$13000.00}. When he came back on the phone he backtracked and was explaining that I owed money for various amounts and that is what took my payment 'down ' to {$120000.00}. Again he backtracked when I told him that this was not what he said. I then asked him how I owed money if I made a lump payment of {$13000.00} which pays me forward through the end of XXXX or early XXXX. He then began to tell me that I owed 'simple interest ' on the loan ; I explained that simple interest on a {$1600.00} balance could not be the {$700.00} interest payment that they say that I owed. This would mean that I accrued {$700.00} in interest on a {$1600.00} from XXXX XXXX until XXXX XXXX. Since I did not feel that he provided an adequate explanation for this amount, I requested that he send me a written explanation detailing the reasons why I am late with my payment though I made a lump payment of {$13000.00} in XXXX. I never received that letter but I continued to receive telephone calls from Santander representatives who could not explain the reason that I owed money but who would simply state that I owed 'simple interest. ' I would request something in writing during each conversation about monies owed but I never would receive anything in writing. Instead I would receive a telephone call demanding payment. Yesterday I informed the Santander representative who called me that I wanted XXXX things to be done : 1 ) written explanation of why they stated that I owe money at this time 2 ) cease-and-desist from calling me. I told her that I did not want them to call me anymore because I am not getting the help that I need and that they were not following through with providing written documentation that I am requesting during the telephone conversation. She promised me XXXX things : 1 ) an emailed billing explanation TODAY which was yesterday 2 ) no more telephone calls. I waited again for her to provide email documentation regarding any monies owed but I never have received anything. I need your help determining why Santander says that I owe money, that I am late with a payment, how simple interest on a {$1600.00} loan balance could amount to {$700.00} in XXXX months and why they can will/can not provide this documentation in writing.