Virgin Media drilled a hole that now has mould growing around it, what should we do?

I would recommend getting it checked as the hole may not have been filled with clear silicone when done and water from the outside may have run down the external wall and caught the cable and travelled into the internal plasterwork , you could seal this yourself just with clear silicone making sure the hole on the external and internal is water tight but sounds like it maybe to late as the plaster has already started bubbling