It had said Foreign Secretary Dominic Raab was too busy to speak to his Afghan counterpart, with a junior minister being asked to do so instead.
But the Foreign Office now says it "was not possible" to arrange the call before the Afghan government collapsed.
Mr Raab has rejected demands from opposition parties to resign.
Dominic Raab must resign. If he does not, the Prime Minister should finally show some leadership, and sack him.
He wasn't just asleep at the wheel. He was wilfully complacent and will go down as one of the worst Foreign Secretaries in history.
Over the last 24 hours,Raab's twitter feed is full of updates about telephone calls he has made relating to Afghanistan.
Before that, Afghanistan is barely mentioned. Too little. Too late.