Go back to that testing service counter, ask for the name of the person who tells you to call back, ask for their supervisors’ name and a business card, and tell them that you are going to call your regional FAA flight standards district office and file a complaint about them (give the actual name of the office by looking it up on this link):
www.faa.gov
They are not providing you with a test for an airman's certificate that the FAA has contracted them to provide, and as a result they are delaying your certificate because of their disservice.