Q: iCloud password

I have changed my iCloud and apple ID a few times with different passwords on different devices, all on apple devices. I still get fragments left when using my current Apple ID. Things like error in iCloud or password not Valid keeps popping up.  I currently Only use my MacBook and iPad..How can I purge all these past user and passwords and  start start over with one password/one iCloud account and Apple ID. The Apple reps told me that I have a two different accounts that are recognized as the same person, me.