List all your services:

$ launchctl list

List a specific service:

$ launchctl list | grep "my service"

The result will be in the format PID / Status / Label. If PID is marked as "-" then the service is not started.

Get infos about the service:

$ sudo launchctl procinfo <PID>

or get path and domain:

$ sudo launchctl procinfo <PID> | grep -E "(domain|path)"

Now that you have the path to the plist file (path => <PLIST FILE>) and the user under which the service is started (domain => .user.XXX. => <UID>), you can disable the service by two ways: disable per user or disable systemwide.

Disable per user:

$ launchctl disable user/<UID>/<LABEL>

Disable systemwide:

$ sudo launchctl unload -w <PLIST FILE>