Hi, sorry about this incident but VOs sometimes call referees to verify the work history and applicant's responsibilities. They usually call the phone numbers on the company letter used for your reference letter, the numbers in the attached call card or the numbers on your company website. If your referee did not acknowledge that you did the duties stated in your reference letter when he was called or if your HR did not confirm the information given in your reference letter when the VO called them, this could lead to the rejection of your application. VO verifies job information through phone calls and physical visits to the applicants work place. Hope it works out for you.