Santander Consumer USA Double billing, double billing Fort Worth, Texas

I had Santander Consumer USA take over my loan from HSBC in April of 2010. the first payment I made over their web page double billed me. I called them to try to work something out and either cancel or get a refund so I could get grocery money, and they were completely obstinate about it. They claimed that I had entered 2 payments of $500 each at both 5:08pm and 5:26pm. I asked them why would I schedule 2 payments within 18 minutes of each other for the exact same amount to be taken out the same day? They wouldn't hear anything else about it. I mentioned that I would contest the transaction with my bank, and she said "a bounced transaction can lead to repossession of your vehicle even if the payments are up to date, and it will incur an additional $350 charge for the bounced transaction." She basically said if I disputed the charge, they'd repossess my car. The woman actually hung up on my when I asked for a supervisor. The same thing happened again the following February (a week and a day ago as of this note) with a slightly smaller payment. They were exactly as obstinate about it the second time around.  I filed a complaint with the BBB and am filing a small claims suit for the overdraft fees they incurred. I'm also going to spread as many complaints about them in as many places as I can.