Two words: extremely unprofessional.
The manager/head of global staffing needs to do a better job at her job. Not once, but TWICE (after the phone screen and then onsite), I was constantly following up, just to receive nothing but silence. If this is the way you treat your candidates/potential employees, you're essentially just driving people away. I understand that you may be too busy to respond to every email, but creating a really great candidate experience is just as important for the future of the company. I hope that someone in the staffing/hr team sees this review as they need to get their act together. Otherwise, all their potential candidates will get tired of waiting around for them and accept offers at competing companies.