How stupid does this Company think we are?

Wrote to them advising of a change of address. Within the letter I gave my date of birth, old address and another couple of snippets that only they would have known, let's just say that my signature had an added twist! Lol

Bottom line they have now written to me at my new address asking me to write to them again confirming my signature and giving them a few telephone numbers on which they can harrass me (Alright, they didn't actually put that last bit as such, but that would be their intention) Apparently they cannot write to me without it?????

Needless to say, they will not be getting any letters from me, only a lbaicon as I have tackled them before successfully.