For gTLDs : You may initiate a complaint at https://www.icann.org/compliance/complaint
For ccTLDs : In general, if you claim inaccurate domain holder's contact information, you may initiate a complaint at the respective registry.
For gTLDs : You may initiate a complaint at https://www.icann.org/compliance/complaint
For ccTLDs : In general, if you claim inaccurate domain holder's contact information, you may initiate a complaint at the respective registry.