Knowingly overbilled by Plusnet - Check your bills carefully if you call NZ

[#1]

I recently changed to plusnet for my home phone after being with them for many years for broadband. One of the reasons was the international calls to New Zealand where my sister lives, included in Anytime. However for the last two months I have been charged for the calls, the explanation was that New Zealand calls were coming through as some Islands somewhere due to faulty BT information and it would be rectified as soon as possible.
Surely it must be against some law somewhere to knowingly overbill a customer, and surely Plusnet MUST be able to credit the bills somehow.
Is anyone else affected? Does anyone else feel this is a pretty poor situation? I've now stopped calling NZ until the situation is rectified, not happy. 

[#2]

We're due to make some calls there soon so will have to watch out!
See my reply to your other post as it seems to have been a known problem for a while now 

[#3]

Where as other peoples calls aren't updating I'm actually being overcharged, I can't believe they can't put a credit on my account. Rubbish