I put
0845 161 0019 and
"0845 161" into Google and it threw up a few other pages with 0845 161 00xx numbers on which are linked to information technology:
I wonder whether these have a connection with Sitecom support or whether it is just a coincidence that they use similar numbers.
The 0845 161 0019 number has a burst of ringing tone that isn't native to the UK, so I suggest that calls are answered abroad.
The TomTom 0845 numbers don't have any ringing tone before they answer, so maybe they are not connected to the same company or at least not answered at the same place.
The above is just a thought. Perhaps someone else could look into whether these might be useful leads.