@Shari: do you still have the proof that you went to the Hoorn branch office and asked them to change you adress? If so, then I don't think the collection agency (I assume the Dutch translation for this is 'incassobureau') has a leg to stand on. Wrtie them another e-mail and if they don't do anything, if you've paid for one of the voordeluren-abonnementen and you have proof, then let them worry about it. :
@Dries Bakker: sorry, but that's just a nasty, @#$%& snide-remark. You don't even know this person, so how do you know this person can't speak/write Dutch? And your comment isn't even about the complaint. Typical anti-social forum post.