twice in a year is a bit excessive mate. Are you throwing out statements and leaving them intact etc? People can and will go through your bins for this information.

Are you being careful online, i.e. not filling in your details when you recieve emails asking you to etc.?

If they have phone bills to pay then they obviously have contracts, which requires having an address on file. If you buy online you still need an address, as the handset has to be delivered.