Is there any to permanantly remove this stupid ERRONEOUS message about connect charging cover?
Yes. It is down to a process
/system/app/PopupReceiver_M/PopupReceiver_M.apk
That process listens in for 'important' system events, such as end-of-charging, boot-finished etc and shows a 'helpful' popup to say so.
The AT+T version and the EE UK version don't have the 'do not show again' checkbox, so you have to remove that .apk file above (or preferably rename it to PopupReceiver_M.apk.bak).
You can easily do that if your phone is rooted.
If you don't want to root your phone, you can do it by booting into TWRP, using the 'mount' option to mount the /system directory read-write, and then using 'Advanced' and 'FileManager' to remove/rename that file. Reboot the phone and all will be well; the messages will be gone.
I say 'booting into TWRP'. I can't give step-by-step instructions for this, as I don't know your experience level, and what you have already installed.
As the phone doesn't get rooted, AndroidPay etc still work and SafetyNet doesn't get compromised.