Problem reformatting Mac OS 10.15.1 (19B88) MacBook Pro

Problem (re-)starting up Mac OS 10.15.1 (19B88) MacBook Pro

I wish to turn my Mac OS 10.15.1 (19B88) MacBook Pro computer into factory settings, but I have run into technical problems. The reason for starting the process is that I ran out of memory in my Mac, even I have deleted all my personal files and folders from my Mac. 

I have discovered multiple SW problems after I started the process of turning my MacBook Pro into original factory settings with my Mac. 

Following Apple’s instructions (https://support.apple.com/en-us/HT208496), I used macOS Utilities tool to 1st erase ”Macintosh HD - Data”. I then continued to erase "Macintosh HD” as instructed. This latter process was unfortunately terminated with technical problem and the alert: “..could not unmount disc.. kextcache 69888”.

I tried running 1st aid on Macintosh HD with the following alert:

Running first aid on “Macintosh HD” disk2s5

Repairing file system

Volume could not be unmounted

Restoring the original state found as mounted

The repair cannot be performed because on or more volumes are mounted. : (-69565)

Operation failed

Followed by similar alert on running first aid on “Container disk2”:

Running first aid on “Container disk2"

The repair cannot be performed because one or more volumes are mounted. : (-69566) 

Operation failed

Now I am stuck in the Disk Utility mode as I cannot move out from disk utility mode by restarting my Mac due to the fact that the following alert starts refreshing in a loop (on a black screen, white collar text on top of white colour "turn on/off" sign) without disappearing away:

“Your computer restarted because of a problem. Press a key or wait a few seconds to continue starting up”. 

A new try to erase “Macintosh HD” and creating “Macintosh HD” failed with the following alert:

Erasing “Macintosh HD” disk2s5) and creating Macintosh HD”

Preparing to erase APFS volume content

Checking mount state

The volume “Macintosh HD” on disk2s5 count be unmounted because it is in use by process 725 (kextcache)

couldn’t unmount disk. : (-69888)

Operation failed

Your tips, advice and help is highly appreciated :) as I am not very technically savvy.