If you're using the pre-defined muxes, remove them and add a couple of muxes manually & tvh should find the rest. If you can't find any frequencies online use w_scan to discover the tuning params.
sudo apt-get install w-scan
sudo service tvheadend stop
sudo w_scan -ft -cfr > channels.conf
--- Once complete ---
sudo service tvheadend start
replace fr (france) with your current country code.
If you don't get anysignal ok messages with the output something else is wrong.