These two scans check different things. The NT scan is done earlier, around 11 to 13 weeks, and the quadruple test later, so normally both are offered rather than one replacing the other.
Next Steps
Confirm directly with your doctor whether the NT scan was deliberately skipped, and if you're still within the window, ask to get it done.
Health Tips
This scan has a narrow time window, so don't delay clarifying it.