iCloud spyware software access

My account has been compromised by one of the Child Tracking software programs, Using my UserID and Password for my iCloud Account. They have logged in and have access to my iCloud account. I've no idea how they managed to get into the account. But its happened. I know this is the case as certain person has all but told me they have done it. I've set false information traps that have confirmed suspicions.

On looking there is a number of child tracking software out there, that all they require is username and password of iCloud account and a few moments alone time with devices. Once set up there is no software on the iPhone or device. Everything can be seen, keyloggers, camera access. Access to emails, contacts etc, etc, full tracking.

How do i get around the cycle of keyloggers and changing the password. Will changing the password revoke access to these 3rd party programs that have access?

Any thoughts you can provide on this would be appreciated. Any ideas on best practice going forward?