Address: 2850 Long Beach Blvd., Suite 189, Long Beach, CA 90806 Phone Number: (800) 642-8004 -- In the medical billing and receivable management industry, experience pays, literally. Medx Medical Billing Service, Inc. has been maximizing the collections of our clients for more than 20 years from the same location in Long Beach, California. We know that the physician practice is our greatest asset, so we work closely with physicians and their staff to ensure continuity of work flow.