The pair, who played for their country in the 2013 World Cup, had agreed one-year contracts for 2014 subject to receiving clearance.
They are now expected to join up with the PNG Hunters team that will play in the Queensland Cup this year and Robins chief executive Mike Smith says they will do so with the club's blessing.
"When we agreed the deals with Enoch and Francis it was always on the basis that they could get a visa and work permit," he said. "Unfortunately, despite a lot of hard work from everyone involved, that hasn't happened and the decision has been taken to release them from their contracts.
"It is a shame as they were looking forward to trying their hand in this country, especially given the strong links we as a club have with Papua New Guinea."