Santander Consumer USA Holdings Inc Consumer Loan Complaint

Santander Consumer USA Holdings Inc Consumer Loan department,

Vehicle loan Taking out the loan or lease California

I have been paying $540.00 a month for a car - - - 2014 my Apr is 18.10 % for 72 month for over two years since I bought the car. Something wrong with the calculation. From my under standing 18.10 Apr is way lower from what I remember. Cash down payment is $4000.00 plus rebate $2000.00 monthly is $440.00 not $540.00. Please help. I also demand a copy of all documents I mean all even a receipt of my down payment they have nothing to give me.