@8894db4ac916 the W-4 mimics the tax return.
So by switching from Single to Married, the W-4 follows the standard deduction and tax tables for a Married Couple. Therefore, the withholdings are less.
It is quite possible that if your income would produce a refund (including the impact of the child tax credit and EITC you may be eligible for), nothing is withheld because you are still due a refund in April.
In that circumstance, withholdings are returned to you in April all you did was create an interest free loan to the IRS.
It is highly unlikely that Payroll is incorrect; it is more likely that your income is low enough that no withholdings are required and you still will receive a refund in April.
