Martyn and Kay Tott forfeited their prize because they failed to meet the 30-day cut-off point for claiming on lost tickets.
The couple, who bought the ticket in St Alban's, Hertfordshire, told the Sunday Mirror they had already planned how to spend the money.
And they called on Camelot to give them their prize.
"They know we're the winners, we know we're the winners and they should pay up," Mr Tott, 33, told the newspaper.
The Tott's misfortune makes their £3,011,065 prize the largest unclaimed amount of money since the National Lottery began in 1994.
Six-month delay
The Totts did not realise they had won in a draw on September 6 until March this year.
They told Camelot that they thought they had won within a 180-day deadline to claim the jackpot.
But lost ticket claims must be made within 30 days of the draw.
Camelot sought legal advice but decided the game's rules would not allow them to pay up.
The money will go instead to good causes.
The couple say they waited more than six weeks for a decision.
Liberating experience
"Camelot have torn us apart," Mrs Tott told the newspaper.
The 24-year-old said thinking they had the money was liberating and the reverse devastating.
"It drains the life from you and puts a terrible strain on your marriage."
"It was the cruellest torture imaginable.
She is outraged at Camelot's attitude.
"It's not as if they can't afford it. How can they talk about the integrity of the lottery when we've been mucked around like this?"
Camelot said that the rules had to be observed.
Counselling offer
A spokeswoman said the couple had declined the offer of professional counselling.
A spokeswoman said: "We offered to keep them informed and meet them very regularly - but two weeks into the process, they said don't come back to us until you have a decision."
"At no point were they given any encouragement that they were to be given the money," she said.
She added that the lottery had taken legal advice, as had the watchdog, the National Lottery Commission but there was no discretion allowed in the rules.
"The rules stand. The game and the National Lottery must abide by the rules."
The ticket numbers 6, 7, 11, 23, 32 and 44 were the regular ones used by the couple.