LG D390n / F60 – fastboot only

Got that phone that way, according to customer it happend after OTA update. Phone basically boots straight to fastboot mode and nothing else. When forcing download mode i get "secure booting error". None of the known commands work in fastboot so i can’t flash LAF or any other partition, it always ends with "unknown command". It also doesn’t respond to "fastboot reboot" (nothing happends) etc.

Anything can be done with that?