In Kodi, if you go the the Channels screen of the TV section, it defaults to sorting by channel number. However, if you open the options menu there ought to be an option there to set the sort based upon the name of the channel.
In the Guide view of Kodi, however, channels are only displayed by number. Likewise with the OSD Channels display, IIRC.
You can mitigate the numbering options one of two ways. Firstly, you can renumber your channels in Tvheadend so that they are numbered based upon he name sort. Or, you can use Kodi's channel manager interface to renumber your channels. The first option would affect all clients connecting to your Tvheadend server, while the second would only apply to that particular instance of Kodi.