Hsbc Auto Finance HSBC Finance They are charging me additional money after my 72 pmts on Auto loan are ALL paid in FULL. Carol Stream, Illinois

I purchased a car (2003 Buick Century) with HSBC Finance in Oct 2003. The contract states 72 payments for a total of 6 years. In the past 6 years, I was 15 days late on my payment ONLY 2 times and did pay the late charges shown on the payment the following month. I also requested an extension twice in the 6 years so my final payment was 2 months later than in the contract. I followed all the guidelines for the late pmts and the extensions and was NEVER told there would be any other fees incurred for the late pmts or extensions. My last payment (72nd) was paid in Dec 2009 but HSBC now tells me I still owe $1130.52. I spoke to a rep on 1/4/10 (after receiving a bill for Jan 2010) and was told that was the amount due because of the 2 late pmts (which she acknowledged I had paid late fees on) and the 2 extensions, I incurred this additional amount. There is nothing in my contract that states this and NO ONE EVER said anything about this additional amount being due for late pmts or extensions. I am furious and want this loan to be paid as of Dec 2009 as it was stated in my contract after the 72 payments were paid. I am a single (almost senior citizen) person and cannot afford this extra amount that is not due on my loan. I met my obligations and paid all my payments even at times when I could not afford food. I want the company to meet their obligations and mark this loan paid in full as my contract stated. I have a copy of my contract if necessary to show the payments etc. I am also sending copies to the Attorney General, Consumer Affairs and Call For Action regarding this matter. 

I have tried to work with the company, but they just insist this is due even though it isn't/wasn't stated on my contract or when I requested the extensions etc.