They have psychological issues not behavior ones that prison will serve them for the right purpose. Prison will rather as you mentioned escalate the addiction. They need to be in some rehabilitation center where their addiction is analyzed and they are given treatments along with therapies that could help them in overcoming the bad thoughts they have. They are not criminals rather they shall be treated as mental patients.
Indeed, they are having some psychological problems, and needed to be asess by professionals , gambling is good for fun, and for creating money, but in moderation because if not, it will only lead to a bigger problem that can affect not only themselves, but also to those people who are in their environment. Addiction is too hard to stop, especially if it is too long before that person is aware that he is an addict. Family and friends should help him and distract him with other things.
Gambling addiction is worse and it also hard to control but I'm the type of person that believes prevention is always better than cure because if a gambler is aware of addiction consequences such gambler won't dare put what he/she precious most on the line. Therefore, i think gambling company needs to showcase on their site proper awareness to their users.