Bad Repo Tactics Invalid Contract?

I purchased a 94 jeep from a used car lot in maui in 2005, for about $6000 over a year of making payments ontime all the time i fell behind when the jeep starting having major problems. When the dealer contacted me about the payment. I informed them that i had hard times because i had just replaced brakes, air intake & filter, and stil had to replace several other parts just so that i could get a saftey and register the vehicle. I also informed them that the radiator had a big leak and needed to be replaced this was my biggest thing. They said that they could fix it at their shop so that i would have a running vechicle as long as I paid for the towing and cost of repairs verbally estimated at $200. They said that they would have my vechicle back to me with the radiator fixed by the following friday. I went in the following friday and Paid over $400 wich was the cost of tow & repair & partial payment. to get my jeep back. They said that they were waiting to see if i would pay before they would start work ( not what we originally agreed to). Two weeks went by and i called them to see if the jeep was fixed. they said they were still working on it. Over a month had passed and then they finally called me stating that the jeep was done and if i wanted to pick it up i would have to pay $800 to get the vehicle back. I asked to speak with the owner who I set up the agreement with and he refused to talk to me. Over and over again i tried getting in touch with him and he would refuse my calls or not call me back. a week later I got a call from a credit agency stating that it had been turned over to collections.. I am now furious and don't know what to do I only owed $1500 of the original 6000 and they took my jeep for repairs to 30 days to fix it and then repoed it casue they wanted more money. when you calculate it out thats $1200 in a month for a jeep whos payment was only about $250 a month. I also found out from looking at my jeep contract that I am listed as the seller and they are listed as the buyer ( can i use this in any way?) It's not that i don't agree with them about the $1500 owed it's that they held me hostage and are still currently doing so to get money.

Please help i dont know what to do