Halitosis may not only be due to Oral hygiene. If you have just done scaling and your dentist has ruled out oral hygiene issues then you need to check other things. Upset stomach, acidity issues and ENT problem like sinusitis can also cause bad breath.
Next Steps
Treatment depends on the cause so get an accurate diagnosis.
Health Tips
In the meanwhile sip water or other liquids to prevent the mouth from drying. You can chew
sugar free gum like orbit. Continue brushing twice a day and floss if possible.