If you suspect works have been carried out without Listed Building Consent you should contact your Local Planning Authority immediately who will be able to advise you on how to proceed.
Os ydych yn amau bod gwaith wedi'i wneud heb Ganiatâd Adeilad Rhestredig, dylech gysylltu â'ch Awdurdod Cynllunio Lleol ar unwaith a fydd yn gallu rhoi cyngor i chi ynghylch pa gamau i'w cymryd.