That is so strange. Are you using OpenWeb? I use Nexus and I do not recall having problems. In fact, I don't use the local at all - what I find is that I can go well over my international cap and international continues working fine (I hit 13GB international on a 10GB account this month... the only reason I stopped is because I had another 10GB account to put to use!)
I would definitely find out from the ISP what is up, because you are supposed to be getting like-for-like local cap with the product!