If your waiver request is denied after a personal conference, you will need to ask for a hearing in front of an Administrative Law Judge (ALJ). You must ask for the hearing within 65 days of the date on the denial letter. Asking for an ALJ hearing on your waiver request will not stop Social Security from taking some or all of your check to repay what you owe.
If your waiver request is denied and there was no personal conference, you will need to ask for a reconsideration of your waiver request. You have 65 days from the date of the denial notice to ask for reconsideration of the waiver denial.