Generally when you sell your home and you taken a first time Homebuyer's credit in 2008, You need to pay the remaining balance on your first time Homebuyer's credit in the year you sold your house. For an example, if you sold your home in 2014, you would had to pay the remaining balance of $5000 in 2014.
My suggestion when you fill out your return this year, indicate you sold your house in 2019. Turbo Tax will calculate the remaining balance and you will need to pay the remaining balance of your first time Homebuyer's repayment. I suspect when your taxes were prepared in 2014, the preparer did not properly report that you sold your house in 2014. As a result, from 2014 until now, you have been repaying that $500 as if you still owned the house.
Please review this Turbo Tax link that verifies the information that I have just given you is correct.
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