A few years ago I had a car financed through GM financial, that car was repo'd and I was sent a bill for a little over $1,000, that amount eventually made it to a collection agency and reported on my credite for about a year.. I recently paid that amount and it was updated that the account was paid charged off, a month later I got a notification that GM financial is now reporting I owe them $5,000. 
How is that possible, for over a year I recieved constant letters saying I owed them 1,000 and now as soon as I pay that they send me a bill for 5k, what should I do to resolve this? because I dont think its fair to pay when they never told me before that I owed them 5,000
Starting Score: 502
Did you keep that info from prior about the 1K? You might need them to validate the debt as to how you now owe 5K.
Yes I still have it, when you say validate do you mean dispute? Because I have already done that