I have a World PrePay account with Orange, which should be charging me 0.03/min for land line calls to Europe. However, Orange has been overcharging me on long distance calls for several months. Most recently, I made a call to France which should have been 0.03/min, but instead charged me 0.60/min -- 20 times more than it should have been. When I called yesterday to complain, the agent said they couldn't access "recent" calls. Today I called and the woman seemed incapable of understanding the problem. Then she said she couldn't fix it, but would speak to her supervisor and call me back.
I found similar complaints with Orange at this thread: Orange mobile billing - charged double (again)
Previously I had noticed my balance depleting faster than I had expected, now I wish I had been vigilant earlier. My advice is to watch your balance very carefully (you can get a prepay balance update instantly by dialing #121#).