I want t refinance my auto loan my Apr is %11 right now how can i reduce it?

I bought used certified car from Dch honda. That is Honda civic 08. The problem is i didn't put any down payment on that and that vehicle is on my mom name and i am co-signer,because she had good credit history and i didn't have any history.And they give us %11 APR. My 14,000 going to cost me more than 24000 dollars. now i recently get credit card and i am trying to make my credit history good.But still my history is not that much good.So my apr is very high is their any way to reduce it what is the best company to refinance it. I already applied to refinance it from my Bank but they denied it reason was (collateral damage) I don't know what it means :(