Cutting it off at the roots is not the full answer. You also have to pull up every bit you can find because it puts little sucker roots down wherever it can and grows all over the place to the detriment of all the other plants you want to grow. Sorry ladybird, hope I haven't started you crying again, but it is a menace. My grandson dug the roots out and it is still growing everywhere it can get its little sucker roots down, including up the walls. Drastic measures are required constantly.