Unable to complain to Virgin Media as a non-customer

Virgin Media visited my house when I wasn't there and put a cable through my garden and path - damaging my path and filling the channel with cement. They also put a box on my wall. My house is being sold and the future owners ordered the cable for when they owned the house. The engineer installers were told by 2 neighbours not to install this as they knew we didn't want this as we had already sent them away 2 weeks earlier. My neighbour also gave them my mobile number to ring me asap but they chose to ignore this. This was wilful trespass and they damaged my property. 

I managed to contact customer services who promised a call back within 48 hours - of course they didn't phone back.

Does anyone know where to send a solicitors letter as I want compensation to replace the path and remove the cable and box.

Looking at previous messages Virgin Media has Customer Services by name only.