We had this horror in a small garden and did get some control by first dousing it in strong weed killer and then pulling and digging it out then cutting off every little shoot that appeared as soon as it appeared. You must cut off any green growth immediately to stop it feeding the roots. Eventually the roots will weaken and die but it can tak e a year or two. You may think you have dug out all the root but unless you need a ladder to get back out of the hole left behind you probably havent. They go down for miles. Good Luck