We have one DC together, who sees my EXP through a contact centre (long story, I will give details if relevant!)
EXP has recently moved, and doesn't want me to have his new address. (He always thougth the world was out to get him
- as if anyone would actually bother!) However, our DC wants to write letters to him. EXP has now given our DC a FALSE new address. It doesn't exist either on Google or Royal Mail. 
The likeliest explanation is he's trying to dodge the CSA, but I also worry that he may at some point try to persuade our DC to move in with him, or possibly abduct DC. (In fairness this is not very likely, but still.)
As DC do not have any contact at his new address, do I have a case to ask him his address, or should I just respect his privacy?