All five numbers and the Thunderball were matched in the draw on Wednesday 2 April 2014.The winning Thunderball numbers on that date were 11, 18, 21, 29, 30 and the Thunderball, 4.The ticket-holder has until Monday 29 September 2014 to make their claim.If no-one comes forward with the winning ticket before the prize claim deadline, then the prize money, plus all the interest it has generated, will go to the National Lottery Good Causes.A National Lottery spokesperson said: "We're desperate to find this mystery ticket-holder and unite them with their winnings - this amazing prize could really make a huge difference to somebody's life. We're urging everyone to check their old tickets again or look anywhere a missing ticket could be hiding."Try checking in the pockets of clothing, in wallets, bags and down the back of the sofa - someone out there could literally be sitting on a fortune! We have the champagne on ice and our fingers crossed that the lucky winner comes forward to claim their win."Anyone who believes they have the winning ticket for any of the National Lottery draws within the 180-day deadline should call the National Lottery Line on 0845 910 0000.