Customer Centre number doesn't go through!!!!!

I actually had a good experience with Fedex previously but now I am so disappointed. I have been trying to contact the Customer support the whole morning but it get to a point were it just hangs up! I tried to call the Edenvale reception and firstly I was through but when I asked for an agent I got disconnected again. There is an issue with my Customs Invoice t where they added a substantial amount to the total cost of my package and that needs to be solved but who do I call if I can't call customer service? This is disappointing to say the least. I have emailed the agents that sent the invoice but they do not respond and I want my issue to be resolved before they send back my package or destroy it due to their error!