If you wish to report an untaxed vehicle contact the Vehicle Registration Office, Untaxed Vehicles, Long View Road, Swansea, SA99 1AN.
Os byddwch am roi gwybod am gerbyd heb ei drethu cysylltwch â'r Swyddfa Cofrestru Cerbydau, Cerbydau Heb Eu Trethu, Long View Road, Abertawe, SA99 1AN.