Hi there!
Error code 8002f994 is telling you that the data is corrupted.
You already tried to do the update with a USB device.
This most of the time means that the Harddiskdrive is bad and need to be replaced...
I would do this first! Just replace it for a known working HDD or SSD (or a new one) and this should solve it.
I recommend to replace it for an SSD anyway! This because an SSD is faster, less power consumption, most of the time more reliable etc.
Here is the guide: [guide|3223]. It's very easy to replace it!
You can download the software here from the official Playstation website: https://www.playstation.com/en-us/support/hardware/ps3/system-software/ (scroll down to "How to reinstall PS3 system software" and open it from there.
If you have any further questions, please feel free to ask!