[David]

AC power has to be on a grid so there's likely one transmission and distribution company even if there are multiple electricity suppliers so you just need to call the local T&D company.

Look at where the wires attach to the poles. Are there insulators which would indicate they are electrical lines and not cable or phone lines?

BTW, power lines will kill you. The company that maintains the line is likely responsible for making sure they are clear of trees so they should come cut it for free. If they won't come out, tell them the wire is on the ground and they should be there pretty fast.