I have had similar experiences so I tracked their number to:01158712827 which gave an opt out option. Also it may be worth registering a complaint here: wwwDOTconsumersDOTofcomDOTorgDOTuk//2012/10/tackling-nuisance-calls-and-messages/ (I'm new to the forum so I can't post the link so maybe another poster will oblige) There is a very quick form to complete and the more people who complain the quicker it'll get them shut down