Product: Vehicle loan or lease

I purchased a pre-owned vehicle in XX/XX/XXXX through a car dealership and my loan was financed through XXXX XXXX XXXX. Each month, I made payments on my loan, on time, and for more than the minimum payment, in an effort to pay my loan off early. In XX/XX/XXXX, I received a statement saying I owed {$0.00} for the month, and called the company to inquire. I was told that, because I had been making payments for more than the minimum, I had paid my loan to the point that I had no payment due that month and was actually ahead in my loan. I continued making payments through the end of XX/XX/XXXX and early XX/XX/XXXX - some months even sending more than one payment, again, in an effort to pay my loan off early. 

In XX/XX/XXXX/XX/XX/XXXX, I began receiving daily phone calls from the company, telling me that I was behind on my payments. I told them there was no way I could be behind, because I send payments consistently each month, and was informed at this point that they had applied another customer 's payments to my account in error on multiple occasions ( 5 times in total through the life of my loan ). They informed me that the {$0.00} statement I had received was a mistake, and accused me of intentionally not making my payment, and accused me of knowing that the incorrect payment was not mine, even though I informed that this was the first I had heard about incorrect payments on my account. 

In late XX/XX/XXXX/early XX/XX/XXXX, myself and my son called the company to walk through my account history line by line to account for all payments, and at this time a complaint was opened with the company 's complaint department. Even during these discussions, I was receiving daily collections calls, multiple times each day, and was being accused of knowingly not paying, and being deceptive. I feel I was harassed and that they were using abusive techniques to get extra payments out of me. 

My son and I spoke to two separate representatives, and each time we walked through my payment history, they agreed that I was making consistent payments, and they clearly saw that something wasn't right with how my payments were being applied. 
We downloaded my payment history and saw that, not only were there incorrect payment being applied to my account, but were shocked to see that for most of my payment from XX/XX/XXXX to XX/XX/XXXX, the majority of each of my monthly payments was going towards interest, and in some cases, entirely to interest and not to principle. 

The loan was supposed to be 15 %, and as recently as XX/XX/XXXX, I  made a {$480.00} payment in an attempt to stop the harassing calls, but saw they applied {$400.00} of my {$480.00} payment to interest. My loan was for {$10000.00} and over the last two years, I have paid over {$2700.00} in interest, and only {$2000.00} in principle. 

In early XX/XX/XXXX, my son and I spoke to another representative, who agreed that my account needed to be reassessed and advised me that she was going to speak to the complaints department about my account, and that I would not be receiving any collections calls while the account was being researched. I received a call several days later in follow up, and the representative completely changed their tune. They told me I was behind on my account and accused me again of knowingly not making payments on my account, even though my son and I had just walked through each payment with them the week prior. During all of this, the collections calls did not stop. 

I feel this company is using deceptive practices, applying payments in a deceptive way, and using abusive techniques to verbally harass and scare people into making payments unnecessarily. There also appears to be illegal activity in the application of payments towards interest vs. principle. 

I want to file this complaint in the hopes someone will advocate on my behalf and help me have each and every payment reapplied correctly, be refunded the interest so the balance of my loan reflects correctly.