Postman Martin Noble had to flee his home in Carlisle in the early hours of 5 December when Storm Desmond hit.
He thought he had contacted to Cumbria Community Foundation for help, but only realised three weeks ago he had forgotten to press send.
The family has now received help and Mr Noble said "despair" had been lifted.
Postman Mr Noble, who had been living in the city's Warwick Road, said: "We thought that we didn't qualify and that's why we hadn't heard anything.
"I re-sent the application when I realised I hadn't sent it in the first place and I got a phone call the next morning offering a grant.
"On that Saturday in December, a policeman knocked just after midnight and said we had to evacuate immediately. We lost everything - all our white goods and furniture."
The Community Foundation said almost 1,000 families out of the 5,300 made homeless by Storm Desmond were still in temporary accommodation.
It has now re-launched its appeal to raise money for its relief fund.
Andy Beeforth, chief executive, said: "We know that there are people out there who were flooded and still haven't come forward for help.
"We think this is partly because some people still think they are not eligible for a grant or that someone else is in greater need."
Mr Noble, his wife Selina and daughter Daisy are in temporary accommodation in Wigton and friends rallied round donating furniture.
He added: "We had maxed out our credit cards.
"There were so many times we were in tears and wondered how we were going to get through. For so long it was so bleak.
"You can't believe the happiness we feel now."
A flood victim went without financial help for 10 months because he forgot to hit "send" on an e-mail, it has emerged.