Bali lawyer Erwin Siregar told AAP he had been told about the decision.
"The sentence has been raised from 15 to 20 years," he said.
"I heard the (Indonesian Supreme Court) document is on the way from Jakarta to Denpasar now."
Prosecutor Ni Wayan Sinaryati said she had only heard the news from the media and a spokesman for the Denpasar District Court also told AAP that Bali authorities had not received any official word about the Supreme Court's decision.
This follows revelations by the Australian Broadcasting Commission that the decision was made a week ago.
The ABC said her sentence, reduced to 15 years from the original sentence of 20 years, is being reversed by the country's highest court.
Corby was last year sentenced to 20 years in a Bali prison for smuggling 4.1 kilograms into the country in a bodyboard bag.
News of the sentence reversal comes on the same day that Corby's younger half-brother, James Sioeli Kisina, 18, faced a court in Queensland on charges of drug theft and others in connection to a home invasion in a southern Brisbane suburb.
Mr Kisina told the court that he had learned that the property's occupants were allegedly well-known drug dealers could have information that might have helped his sister's case.