I was on Say No to 0870 and found this funny post by:-

Chimpchoker: I was getting a lot of hassle of a number of Credit cards I had defaulted on and one in particular being sainsburies would phone me up to 13 times a day including weekends. They wouldn't listen and in the end I told then to stop telephoning me as it was harrasment and i'd involve the police. The calls reduced to around 6 - 8 a day so I gave them a "new" mobile number to contact me on. I then went Ex directory on the land line but on the new mobile number i forwarded it to a 0901 porn line so every time they rang the number it diverted to the porn line.  
 
Mind you the number of calls went up to over 30 a day for over a week  after that so someone enjoyed themselves......