In my opinion, if you send a DV and receive no reply, rather than complaining, you should actually consider yourself fortunate. If the CA doesn't validate the debt, they can't collect it -- and if my own admittedly-anecdotal experience is any indication, there's a good chance that they won't validate. So far this year, I've sent out four DVs, to four different CAs. Three of them didn't even try to validate, and one of them sent back incomplete information (which is not legally regarded as validating the debt).
I used to send out C&Ds right away when hearing from a CA. Now I don't; instead, I send a DV. If you send a C&D, they're legally allowed to respond with a threat of legal action (if the threat is sincere, that is). However, if you send a DV, they can't do anything at all unless and until they validate.