need to get my credit score up to 600 to refinance my home

I went to the bank 2 weeks ago to refinance my home and add a couple of bedrooms to my home... I was told that I need to get my credit score up to 600 to get the loan... I have disputed a lot that is on my account.. I had 2 account that have been paid off 3 years ago, they are showing up as 5 separate accounts with same banks in 5 different city's... I had 2 medicinal bills I paid off 2 weeks ago how longs will it take for them to come off of my credit report??? They emailed the reporting agencies after I paid them... I received a phone call about 15 min's ago, it was from a collection agencies that they had a old bill, wonted to know if I wonted to work some type of Payment options out so it will not go on my credit record... I asked the girl what was the date of the bill... It was to a local hospital dated December 6, 1999.. Can they still report this to the credit bureau???? thanks for the info
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last question
if the bill was sold for pennies on the dollar to the collections they can collect but not put it on your report or threat to sue.
second question
those should take no longer than 30 days.
some of those duplicate accounts might come off. I would call the original creditor and talk to them about this action. three states or cities or account or whatever and find out if you can get some of that changed. Thell them you will which of the duplicates you will dispute so thye don;t have to do any work juts dont respond.
pay down any balances that might be more than 80% or your high credit limit