I've already had that conversation with them, and they waffle on about the difference between a "Broadcast" and a "performance".
Just tell em you haven't got a radio and that they should go and bother someone else ! they will tell you that they "might" send someone out to check whether you have or not - take a chance !!
You will get one more letter then thats it ! they go quiet and go bother someone else.

Regards
Dave