Galaxy S3 GT-I9300 Stuck at Samsung logo with no recovery and no download mode Background: 

I was having CWM recovery with custom ROM "CyanogenMod" and recently I flashed "LineageOS" successfully but I noticed that phone internal storage is being occupied by previous ROM files and folders so I tried to delete everything to have a phone in clean condition with only "LineageOS" files. By mistake I format /boot, /system, /data, /cache and /sdcard and after that I reboot to system. 

Weird Stage:  (don't know if its soft brick or hard brick) 

:( At this stage, my phone stuck at Samsung logo with no access to recovery mode and download mode. I tried 


Volume up + home + power  = No recovery mode and
just Samsung logo 
Volume down + home + power = No
download mode and stuck at warning screen with a yellow
triangle but pressing volume up is not entering to download mode


:(
 Also, phone is not detected by Odin or ADB in PC with having correct Samsung USB drivers and also tried Kies but phone is not recognized by pc at all. 

I tried some solutions like


flashing debrick.img into SD card and try to boot with it but no success 
pulled off the battery for many hours and after putting it back have no success to access download mode
Tried with different USB cables and different OS like Windows 8, 7 on different PC 


Update: 

With the help of @esQmo_ 

I just found that Volume up button is not working and thats the whole reason why Recovery and Download mode are not accessible. Can I do something directly from SD card to boot into recovery or download etc?
Does your volume up button work? If i'm not wrong, Download mode never fails to boot into. 
Let's assume it is not working and in this case, you'll need a way to force boot in download mode.
There are two methods I could find:


Using a USB JIG (and here)
Using a software called Samsung 300K Tool (Video)


After that, flash stock firmware and everything should work now.

Other solution would be replacing the volume buttons flex cable or making jumpers from the volume contact to the motherboard. Schematic below:



And 


Source: gsmhosting.com