Am I supposed to be charged for postponing my surgery due to a positive COVID test result?

Be aware of the terms of the surgery center you are working with. Personal behavior does make a profound difference to reduce your risk for getting Covid. The costs of not showing up for surgery are real. It means that the surgery facility was not available for anyone else when you do not show up for surgery. Early on, many facilities were waiving all fees for these types of rescheduling. Now that many are vaccinated and understand what behaviors reduce the risk of Covid ( masking, social distancing, appropriately boosted), it is possible to substantially reduce the risk of getting a Covid infection prior to a scheduled surgery by modifying behavior. The surgery center policy emphasizes the need to take responsibility for your controllable behavior prior to surgery to reduce the chance of getting Covid. It sounds like your surgery center is working with you on this matter.