dig as much as you can then use a strong weed killer like SBK [scrub and brush killer] and follow the instructions. you may need to reapply several times. they are a form of grass and as such can be troublesome.

Bamboo is very invasive, it sends out underground rhizomes that are hard to deal with and it's a nightmare to get rid of. Some years ago someone gave me some so called dwarf bamboo. I planted it into one of my borders and It spread like wildfire. I sprayed it as often as I could with a systemic weed killer and it took over a year to completely eradicate it. Even then it was hard to get rid of the dead dry stalks that were left. You can't just pull them up out of the ground as I discovered that the roots grow deep and in all directions. I ended up setting fire to them and burnt them down to the soil.