There are two reasons why the address listed on the WHOIS might not be sufficient for you to contact them:

The information we have is wrong, out of date or absent

Registrants are required to give us "correct" contact information. If you are concerned that the address information for a domain name is incorrect, and you can prove this, please contact our registrant services department about it. We may then start our process for dealing with this, which will result in new information being entered or the domain name cancelled.

The registrant is using the opt-out from the WHOIS

Consumers are not required to show their address on the WHOIS. They can take advantage of an opt-out. This opt-out can be removed if they are found to be trading, and we can also release their address in certain cases. See our advice to registrants on this topic.