Harassing calls and threats

I have a five year loan on my vehicle.  Every month since I bought the vehicle I have a late fee added to my account, even though I may have been late a few times but not every month which adds up to almost 1000 dollars.  Like everyone else on here, one or two days after my payment is due a Cps rep calls my work, my mother, and then finally calls me.  They always assume that I am unemployed instead of the fact that I work my butt off for my family and everything else, and still pay them.  They also have attempted to take 2x my payment at one time, overdraft ing my bank account at least three times since I bought my truck. Two months ago my pay off amount was 1400 dollars, but the payoff was not due then.  I have payed 900 dollars since then.  Now my payoff amount is 1700 dollars. Almost ready to let them come get the truck.