Welcome! The reason it will never work is because (by your own admission), you are an addict. As addicts, we don't have the luxury of stopping one drug, yet using another. Even if we "haven't had a problem" with that drug, we will abuse it until we do. Its great that you addressed your opiate addiction via methadone, but it sounds as though all you do is take the medication.....if you want recovery, you have to utilize your time on maintenance to change your life....which means counseling, support groups, everything you can reach out for.
Recovery never comes via osmosis, reading about it, or other passive activities, you have to do things, many of which you likely won't want to try at first. Using coke, drinking, smoking weed, etc. while on methadone will quickly negate any gains you may have made, add new problems, and eventually lead to the only three outcomes of the disease: jails, institutions, or death. Your best bet is to tell the folks at your clinic that you are having problems and get help!