Assuming that you are in the UK. If it is a nuisance call then that is an offence and should be reported to the police. (I am suprised that the network refused to help.) If it is a marketing call register with the Telephone Preference Service and the call (and all other marketing and sales calls) will stop in about 28 days. If its some one that you just don'e want to talk to look at the Caller ID on the screen, answer the phone and then put the phone under a cushion so you can't hear it - they'll get sick of talking to a cushion after a few times.
Terry, June 2006