You did a great job responding to an "addicted" gambler but unfortunately, his mind is stronger than your words that is why he faced what he must face and it is losing all of his money.
Sometimes, you just need to leave behind an addicted gambler because there are times that instead of letting them stop they will confront you and say bad things. I didn't tried this in real life because I didn't saw anybody who is gambling in my community but I know the feeling of a person trying to stop a gambler for losing more money but the problem is they want to recover their losses so it would be beneficial for you as a helper to just let him do what he wants. It isn't your money though so let him use his money.
The desire to stop gambling must come from within the person otherwise even if you help him and he stops for the time being once you are not around he will begin to gamble again, I have tried to stop some people to keep gambling their money away and as you may guess they did not respond very favourably to it, they told me it was their money and that I had no right to meddle in their lives, and they were right, so I had no option but to watch them self-destruct and I could do nothing to stop them.