At long last I found out how to use uPnP to get status info put of my Frtizbox – as the old script I had used stopped working after the last software upgrade.
And the answer was on this page.
It contains a perl script that list all counters and variables that can be downloaded by using the uPnP protocol.
To use this you can call the perl script like this :
perl upnp.perl FRITZ | egrep GetTotalBytes | head -2
and I got
urn:upnp-org:serviceId:WANCommonIFC1::GetTotalBytesSent:NewTotalBytesSent = 398046387
urn:upnp-org:serviceId:WANCommonIFC1::GetTotalBytesReceived:NewTotalBytesReceived = 2884042651
which is the total number bytes sent and received since last restart.