Repossession: Vehicle loan or lease

I volutarily repossed my car to ALLY BANK becasue I lost my job and could no longer pay for it. They took 2 months to come get the car from my home after I called several times. My balance owed on the car was $18000.00. They repossed the car and sold it for $1000.00. The amount I owe after sale of the car is $18000.00 after inclued fees. Why was the car sold for such low amount when I owed so much on it. The car was in good running condition with no major problems. I also gave then back both keys, They were left in the car. They're now offering me a settlement option of 1 payment $7300.00 or 48 payments of $170.00 which equals $8200.00. I disagree with both because I feel like they could have gotten more for the car whent hey sold it. I can't pay that much for a car that I no longer have in my possesion.They practically gave the car away but I owed over $18000.00. I did receive a letter of intent to sell but not a date or time or location of the sale. I just would like to know why the car was sold for such a small amount. I doesn't seek fair. Thank you