After a long night playing the Betfred Frankie Dettori Magic Seven Blackjack in January 2018, Mr Green's online account was credited with £1,722,923.54 which he tried to withdraw - but the request was declined.
After placing some more bets with his winnings he took a screenshot to prove what had happened. However, a Betfred director called him to say there had been a "software error" and it was rejecting the claim.
As a token of "goodwill" the company was willing to pay £30,000, but Mr Green would have to agree not to talk about it ever again.
Mr Green refused and the company increased its offer to £60,000, which he also rejected.
More than two years later he has gone to the High Court to sue Betfred and its parent company, Gibraltar-based Petfre for £2m, including the interest he would have earned from the win.
Mr Green said "the last two and a half years have felt like hell on earth".
"You wouldn't treat an animal like I've been treated by Betfred," he said. "Hopefully the judge will accept the arguments put forward by my legal team and this nightmare will be over. My champagne remains on ice!"
Mr Green is in poor health and has suffered four heart attacks - one of them since the money was credited to his online account in 2018.