Seems HR is the same all over the world... we call them Human Remains over here and they are dispised by everyone!
If they are renowned for not returning phone calls, put your questions in writing, keep a copy for yourself and circulate a copy to the Vice President of Human Remains (I would also let the VP know the reasons you are sending them a copy of your letter).
Same if you send an email... send a copy to VP of HR. And set your email up so that you receive a "read receipt" when it is opened. Then they cant deny receiving the email. Just a thought... and it bit of ammunition if you decide to take further action
And, as an employee, you are not a "potential
" customer of HR... you are an actual