He should go to small claims court (or the Dutch equivalent) to get his 5 euros back. There was actually a case in Germany where the largest ISPs continously ignored a customer whom they charged too much at some point (similar order as the 5 euros) . The story ended with a court bailiff (?) going into the main ISP office and seizing a printer I believe. Big PR disaster and much higher cost then the original amount.

These big companies do these things all the time calculating on people just giving up. We should take the advantage of the courts to teach some lessons as much as possible.