Product: Vehicle loan or lease

I have struggled for the last year to get Hyundai Motor Finance to service my loan promptly and responsibly. I pay about double my minimum monthly payment every month. The company requires that I call their customer service line every month to apply that overpayment to the principal. Every month for the last year I have struggled with their customer service to get this done. It usually takes XXXX calls to get them to complete the request correctly. There is no other avenue for me to submit this request and no way to do it on their web portal. They refuse to do it automatically unless I make a large enough payment. Sometimes, but not always, they will send me a request ID number so that I can follow up on the request. I have to do this because almost always they will either ; not complete the request at all ; do it incorrectly, or reject the request because it was submitted on their end incorrectly. They do not notify me if the request is rejected, so if I do not follow up I have no way of knowing if they have done it. In one instance they submitted a request to apply my entire last payment to the principal ( not what I asked for ), which should have been rejected but was not. In this instance, it pushed my payment due date back far enough that I had a 'past due " payment date. It would have negatively impacted my credit score had I not caught the mistake the day it happened by checking their web portal. 

I don't understand why they have a policy of not applying overpayment to principal automatically. I also can't get a straight answer on whether overpayment that is not manually applied to the principal by calling in is ignored when calculating interest. I have no idea if this company is taking my overpayment and putting it into some short-term interest-accruing account until my minimum monthly payment is due and calculating interest based on a principal number that only includes the minimum monthly payments. That would be a profitable scam for both the loan servicer and Hyundai Motor Finance. I believe that it would also constitute fraud. I have asked about this but have not gotten anyone who was able to give me an answer that I had confidence was the truth. 

I have spent XXXX hours of my life on the phone with their support over the last year. At the very least the company that is doing customer service is wildly negligent. At worst, it is large-scale fraud. Additionally, they lack the most basic digital security measures. When I get my confirmation number for a request, it comes from the email address XXXX. This domain lacks an SPF DNS record, that record is used to authenticate the sender. The lack of this record will produce a warning message with any major email host that says that they can not verify that the send and in most cases the email will go to spam. If someone wanted to they could send emails pretending to be from this address, and the fake emails would be identical to a real one. This is a super basic security measure that indicates to me that they are so incompetent that my personal financial information is not safe with them. If they were breached I would not even be confident that they have the expertise to detect it, to say nothing about stopping it. 

I am willing to provide documentation to show all this if requested.