While there are undoubtedly several different scams involving 'undelivered parcel' messages there are also plenty of apocryphal stories doing the rounds about people getting massive telephone bills through unwittingly calling premium rate numbers (or through, say, pressing a certain number on their keypad in response to a recorded telephone message). Such things simply can't happen (because Ofcom regulates the charging structure). Calls to numbers starting 0906 66 undeniably aren't cheap at £1.53 per minute from a BT landline but you'd have to be holding the line for nearly 3½ hours to run up a £315 bill.
Further, although the Lancashire Telegraph advises people who receive such cards to contact Royal Mail's fraud section, it might actually make more sense to contact:
(a) the police (
http://www.actionfraud.police.uk/ ); and
(b) Ofcom - who can get the service disconnected.