This is the reason that I have always said that the best way to cure a gambling addict is when the person realise that they are very much addicted and the person involved who is the victim understands that they need help. That is the fastest way to rescue someone who is addicted. If someone is truly addicted, but they do not understand that they are addicted, all the effort you put in stopping the addiction will result to nothing. Thereby rendering their efforts fruitless. That is why it is fine to first convince someone that they need help before rendering help to them.
It's just a general thing. For someone to get corrected when they are wrong in their actions, they must first acknowledge that they were wrong before they will accept the advice you are giving them; otherwise, you are just beating around the bush, and they will still do whatever they have on their mind the moment you just let them go. There was this friend of mine in school who was so addicted to gambling that his parents tried a lot of strategies to help him get out of this addiction, but every attempt was futile, and I know the problem the guy has is that he has not really realized that his habit towards gambling is so terrible; only if he realizes it, then he will limit how he gambles.
Without realizing the mistake there's nothing to expect from the person but to continue playing, they will keep on doing the same routine even their love ones are trying their best to help, though we really can't say whether the person will realize his own mistake and will try to help himself, from that realization sooner or later the help that you are sending will be appreciated and will start to manifest.
Just keep trying if you really love the person and you really wanted to help with the addiction that the person possesses.