Did 2016-2018 taxes with TurboTax and all received a refund. Now, in 2019, it is using all the refund to pay for a 2016 payment. How come this wasn't caught earlier? How come I received a refund and then now it's saying I owe?
You wrote "to pay a 2016 outstanding debt". This was likely an "offset", a program administered by the Department of the Treasury to collect things like student loan debts, child support, and the like.
TurboTax has no way to know if you had an offset. TurboTax uses only the data you supply to create a tax return.
If you want to know why the Offset Program didn't catch up with you earlier, please see https://www.irs.gov/taxtopics/tc203 and call them.
You have to contact the Bureau of Fiscal Services for more information about the offset. Generally, only these types of debt can be collected from your federal taxes:
1. Federal income tax due
2. State income tax due
3. Certain state debts related to repayment of unemployment insurance
4. Child support.
5. Other Federal debts, such as student loans, or anything related to a Federal debt like a grant you had to repay, etc.
Turbotax doesn't know if you had one of these debts, and apparently the state couldn't track you down. Contact BFS, then contact the agency in Texas that claims you owed a debt.