Your original lender almost certainly doesnt own the loan anymore, so not sure why it matters?.

Or should I refinance it at all IF I can put in $500 into principal monthly?

Do both and it will be gone in no time. Check with your current lender, another direct lender (local if your current lender is national) and a mortgage broker and see who has the best deal. For that loan amount you can get your rate below 3.5%, even less if you can do a shorter term than 30 years.

Had about $100k loan left with 4.75% interest rate back in 2009. Should I refinance from the same company I got the loan from? If anybody had a similar situation, what's the estimate cost of closing cost?

Or should I refinance it at all IF I can put in $500 into principal monthly?