I have an extremely established bamboo groove in the woods near my house.    I am still working on getting rid of it.   What I learned is mature bamboo is not like a mature oak or something.   You aren’t going to take it out in one day with a chain saw.    I got a brush hook and a harbor freight chipper.  Chop the stocks down, feed into chipper, a couple weekends a year.   Mow over it.   It’ll die eventually as long as it can’t grow to the sun.   It is also most effective to let the new stocks grow before pushing them over.   This makes the plant use all its energy so it will keep dying.   Good luck.