We had a withdrawal from our paycheck every paycheck to pay extra on taxes. Now we owe. Why?

It depends.  Unfortunately, we cannot see your tax return since this a public forum.  

However, it is possible you just did not have enough withheld on your wages.  To avoid owing taxes in the future, you may want to update your W-4 Form to ensure you are withholding enough in income taxes throughout the year.  You can update your W-4 within TurboTax itself while preparing your tax return by following these instructions.  If you have already filed, you can also use this link to help you update your W-4 Form.  Regardless of which option you choose, you will need to print out the W-4, and submit it to your employer in order to have them make the necessary adjustments to your paycheck.