[the highlander]

1.use saynoto0870.com to find a proper phone number for their head office-demand to speak to their MD or head of customer relations.
2.Complain to OfCom.
If you keep badgering the head office reception sooner or later someone is going to deal with you, especially if OfCom are also on their case.
Log every contact, and everything they tell you, and let them know you're doing it and its all going to OfCom.