Santander USA, Triad Financial Services loans Santander Consumer, Santander Consumer USA Falsified payment check, attempting over-charges, ignores complaints Fort Worth, Texas

I attempted to pay off my car loan Santander 2 weeks ago. The amount owed was $13,451.
I send a check for the amount as my monthly payment. The check was cashed before the due date.
The amount on the check had been altered and initialed by an employee to the amount of $1,345.00 and cashed in that amount.
Soooo......the car wasn't paid off as I'd hoped nor was I notified about the check alteration. I only found about the check
alteration by going to my bank, investigating my balance and the actual check. I had the check printed. I called Santander
'customer service' and complained. I was put on hold for an eternity (one long-distance call). I called back (2nd long distance call)
and was transferred to someone else. This person found a 'copy' of the check somehow and argued with me about the amount and denied
there anything wrong with it and that the payment would stand as it was. He added that the total amount due was now $13,261.00 because a 'revolving interest' charge had been tacked on even though the payment had been made on time and the check was altered.  He told me I should fax my concerns to the 'ASU' department, whatever that is. So, I got all of my documentation together, wrote a note describing my issues in great detail and faxed and mailed (certified mail, another $6.00 spent on this idiocy) the documentation to the 'ASU' departmentas advised. I also filed a complaint the the Texas Attorney General's Office and sent the same information to them. I also included my complaint to AG's office to Santander along with everything else. This all took place 3 business days ago. I have received a return receipt from the AG's office but of course no word from Santander. I plan on taking this to Small Claims Court in two weeks if I don't get the 'revolving interest' fee removed, the car paid off and the title.  I have no doubt I will be ignored by Santander until they have to drag their legal department into it and start threatening me with whatever BS they can come up with. I have time on my hands right now and I'm gearing up for a good fight. Wish me luck!