2009 Buick Lucerne CXL Fuel Pump/Relay

I had the fuel pump relay short out and melt part of
the fuse box, possibly due to having three
teenagers in the back all the time. No recall on
issue, even though it's a well documented problem
with that car and the location of the seat latch and
fuse box, warranty would not cover. Replaced
entire fuse box and all fuses plus notched out the
seat latch so it wouldn't hit the fuse box anymore.
Two weeks later the check engine light was back
on with the same code. Have had it cleared and
reset 4 times now and within 4 days it comes back
on. I'll note that before I replaced the fuse box, I
melted three more relays trying to drive it 22 miles
to the dealership. It also seems to use a lot more
gas and feels like it has a rough idle. Looking for
answers on where to start or anyone else who's
had this problem and a fix. Thank you.