Richs Cars N Credit

I told them I could pay 100 each check and they told me to bring the car back. They didnt say they would make it a bigger problem as they are now I got a letter in the mail stating that they want me to pay 5,000 I feel this isnt right because ive paid more than I should between the cars ive gotten from them one was a acura mdx and the timing belt went out and screwed up the engine and pistions I got it back and I got 10 to 15 engine codes so I told them about it and they got me into a 12 nissan sentra and I feel between the two vehicles ive paid more than enough with this company. They are saying I owe 5,600 and if I dont pay they will come after me and garnish my wages. I dont feel this is right. I have been a good customer......