Apple id constantly asking for password, keeps getting locked

It's been around 2 months with this issue. I called apple support 3 times and they don't know how to fix the problem.

I have an iPad and an iPhone XR . After the problem started, I had to replace my iPhone for a new one (also iPhone XR).

Both devices are up to date. I did everything Apple asked me to do. Updated both iPad and iPhone via iTunes on recovery mode. There were no issues found. I also did a factory reset on the iPad (started up as a new device).

All the settings are checked.

Apps are all updated on both devices.

I don't have the two-factor authentication setup (and I don't want it) as I often work with my iPad and have no access to my iPhone so if I ever need verification on the iPad, I won't be able to enter the code sent to the iPhone as I won't have it with me.

I understand there is a problem with my Apple id but nobody seems to know what to do. Any ideas? Thanks!