that sucks... =*( i'm sorry.
maybe there's another upgrade you can get in the game... or something... but i think hackers that can make 999,999,999 pretty easily would have figured that out by now, lol.
this same sort of thing happened to me when I was buying turnips....700,000 bells gone....... Tom Nook will PAY! ...... or he will be.....ummm....in on heck of a pickle...yaaa...>