If I tell them (via the neighbor) that they have broken it, can they fix it without it being raised back to Chorus?
It's highly unlikely that any contractors on site have anything at all to do with the copper network, let alone the skills to fix it.
Common sense is not as common as you think.
Otherwise call Chorus on 0800 4 NETWORK (0800 463 896) - Option 2. If the Damage is dangerous, choose the Health & Safety option (4) instead.