This is normal practice for these crooks. When you win the line becomes 1.65-1.65. It is quite likely that they will block your account and take your money.
FJ has a history of being a crook. Dunno why people praise them so much. But they are struggling and will come up with any reasons to void winnings and fix their sportsbook lines. I have long stopped playing with them. There are much better casinos and sportsbook out there that doesn't pull the stunts that FJ does.