"slashed off" is correct and can be used in written English.
It is often used to describe a sudden or forceful removal or separation of something. Example: The boxer's trainer slashed off his gloves and threw them on the ground in frustration after his loss. In this sentence, "slashed off" is used to convey the trainer's sudden and forceful action of removing the boxer's gloves.
And when the Jets pursued too hastily toward the sideline, McCoy slashed off tackle.
This month, soldiers slashed off most of it, then stuffed it in his mouth.
Originally embracing a quad rangle, the south and west sides were slashed off by the Brooklyn-Queens Expressway. Brooklyn-Queens Expressway
Maynard, himself a former pirate, ordered Blackbeard's famously hairy head slashed off and hung from the ship's bowsprit.
The pastoral wind-band music, once reflective in mood, is now sucked in and slashed off by the big, loud, tutti chords, executed with frightening precision.
Under the strategy, Alberta saw cuts of 12% in its education budget, 18% slashed off healthcare and 19% from social services.
Oklahoma City thrives on solo riffs from Kevin Durant and Russell Westbrook as they dribble, cut and slash off screens, but the Mavericks knocked them off key from the start.
Because the fin fetches vastly more money than the shark's body, traders slash off the fins and throw the shark back into the water for a torturous death.
As the naked Jews ran shivering from the trains to the gas chambers he would slash off an ear, rip open a belly, or flog them til they fell.
On a recent Manhattan morning, with a cold wind slashing off New York Harbor, Lou Marinoff took the granite steps of the federal courthouse two at a time -- brown eyes fierce, ivory white skin offsetting his dark beard, a Russian fur hat making him the very picture of the engaged intellectual.
They told the story of Chandralekha, a tough woman who "outwits a vicious bandit, delivers the final insult by slashing off his nose and, as a finishing touch, fills the bloodied gaping hole with hot, red chilli powder".
