illegal works

An owner within our building has built a bathroom inside the unit and a cellar under the unit without OC approval.This was only discovered when she was selling her unit. The new owner understandably says that has nothing to do with him.  Is this now the OC’s responsibility to obtain council approval and sign off. we are particularly concerned with the structural beam that have been inserted to hold up the floor over the cellar, the underpinning of some of the footings where she had lowered the level and the plumbing in the new bathroom.