Product: Vehicle loan or lease

I have had this loan for almost 4 years, and everything was fine. I am a XXXX and I get paid once per month - on the last day of the month. I send out all my payments then. My car payment to XXXX XXXX is due the following month on the XXXX, a standard payment of {$580.00}. So, I usually send it 14 days before the due date. I had no problems until XXXX of this past year ( XXXX ). At the end of that month, I received a notice stating that my payment was past due. I called ( XXXX ) and they said they had not received it. I had to make an electronic payment, and then go down to my bank and stop payment on my check. I then sent out my XXXX payment, as usual. Unbeknownst to me, XXXX XXXX  tried to apply the check I sent XX/XX/XXXX to my account on XX/XX/XXXX and it was returned. I again received a notice the end of XXXX that they had not received my XXXX payment. I called ( XXXX/XXXX/XXXX ) and had to make that payment electronically, and again put a stop payment on the check at my bank. I spoke with someone in customer service who said they would send an investigation report through about what was happening to my payments. He also suggested that perhaps the payments were n't being applied because I was not writing the account number on the check, even though I was sending the check with the payment stub. I told him I was sending XXXX 's payment that day and I would make sure to write the account number on the check. I received a form letter back from XXXX stating that my account was current, but nothing that addressed why my payments were being processed so late. I called and discovered that the payment I had sent the beginning of XXXX ( That I had to go and place a stop payment on ) was returned on XXXX - over 30 days after I sent it. I called and spoke with a customer service manager who was extremely rude, and stated that it was the fault of the postal service that they were n't getting my payments. They still had not received my XXXX payment. I called every day up until the XXXX, when it was due. I then had to pay it electronically, and go to the bank and stop payment on my check for a 3rd time. I filed a complaint - and was sent a printout of my payment history - nothing addressing the issue with payment processing. I sent my XXXX payment by certified mail. It was processed on time. I sent my XXXX payment by certified mail. I received back the green card from the post office, indicating that it had been received by XXXX XXXX on XXXX XXXX. In the signature section was a stamp of a person 's name : XXXX XXXX. The tracking number on the envelope was : XXXX XXXX XXXX XXXX XXXX XXXX. Included in the envelope was check # XXXX in the amount of {$580.00} ( my standard car payment ). Today - I opened the bill to pay XXXX 's payment ( XXXX XXXX ), and it shows that my XXXX payment was never received or applied. I called customer service and shared this information with them and was basically told it is n't their problem. The agent did agree to look into it, but now they have my check somewhere and will likely try to apply it 30 days down the road. Thus far, they have reversed the late charges, but I do n't know what will happen this time. I have spent hours on the phone trying to clear this up. I had thought sending my payments certified mail where someone had to sign for them would make a difference, evidently not. I have less than a year left on this loan. The agent told me that I am the only person he has ever heard of at XXXX XXXX that has had this problem. Also - the statement I received for XXXX showed that the payment I had sent for XXXX ( mailed on XXXX and due by XX/XX/XXXX ) was applied to my account and returned as a stop payment on XX/XX/XXXX. This means it floated somewhere in their facility for over 2 months.