iCloud Relock Service was fixed finally by apple. Many people were using this icloud bug related iCloud ReLock Remote Service. To make this work Find My iPhone status must be OFF, and using a online server you actually could make it ON again with new credentials. Service will reply Apple ID and password.
Updated September 2019:
iCloudRelock exploit patched by Apple ( icloud OFF >> ON )
Again, apple just patched the new icloud relock exploit from the same developer in 2018. Now all relock services will be down. this kind of bugs are really difficult to find and rare to see it working in the real world.
iCloud relock was working from instant to 1 min All supported iwatch, iPad and iPhone.
The original developer that found this bug was @minacrisOficial from twitter. Only IMEI number was needed! the API service could enable Activation Lock on your iPhone and send you Login and Password for it. From that moment only who have the relock login and pass would be able to solve your problems to unlock icloud again.
iCloud Relock bug patched
iCloud Relock bug patched on apple servers so is not working anymore. Probably this bug was reported to Apple Bug Reporter, is a web-based tool that developers can use to report issues with Apple software and services, request enhancements to APIs and tools, and track the status of their feedback. To access Apple Bug Reporter, sign in with the Apple ID associated with your developer account.