GPL violation on BongoSurfer

[Pascal]

Hello list,

I would like to report a licensing issue and request for help on how to
proceed. I am the administrator of a project called "bongosurfer"
released under the GPL. It is a program which holds a database of ISPs
for Germany, and allows to establish a modem - or ISDN connection using
a chosen ISP (usually the cheapest). The concept of call-by-call (which
means you can use a different ISP everytime you connect to internet) is
a German peculiarity, therefore our program is used only in Germany. Our
homepage is in German, the sourceforge page is English but not very
up-to-date:

http://www.bongosoft.de
http://sourceforge.net/projects/bongosurfer/


Recently, we noticed a project called "ColorSurfer"
(http://www.color-surfer.de) from a company called "First Internet
Invest LTD". Colorsurfer is a fork of an earlier version of our program,
with some modifications on the source code.

Colorsurfer can be downloaded for free, but the source codes are not
available. First Internet Invest LTD also sells personalized versions of
the program to ISPs who want to provide a dialer program for their own
tariffs. Some ISPs already made use of this offering and provide
downloads for their own version of Colorsurfer, also without sources. We
found this two ISPs, who link to following downloads on their pages
(Linux and Windows versions):

flat2surf.de:
http://www.flat2surf.de/seiten/downloads/colorSurfer-flat2surf.tar.gz
http://www.flat2surf.de/seiten/downloads/ColorSurfer-flat2surf-1-install.exe


1Xnet.de:
http://www.1xnet.de/downloads/colorSurfer-1Xnet.tar.gz
http://www.1xnet.de/downloads/ColorSurfer-1Xnet-1-install.exe

The programs are not really functional, because they obviously did bad
things like sed 's/bongosurfer/colorsurfer/g' on the sources, but that's
another story ;)

We asked for the source codes several times. First time, they sent us
diffs of the sources, but not specifying to which versions of our
sources they apply. The diffs were also very uncomplete. Next times,
they sent us true sources, but they were not complete, not compilable
and obviously not fitting to the released binaries. All the sources were
only for the major release of colorsurfer. Despite our requests, we
didn't receive any sources for the derived versions sold to the ISPs
mentioned above.

How long should we wait to get the complete sources of ColorSurfer and
all it's derivatives? What would be the next step to take if our
requests fail?

thanks in advance for any help offered!

Best regards,
Pascal Pollet