How to kill a zombie lemon tree that just won’t die

Q: I have a Meyer lemon tree that just won’t die. I’ve had it for at least 25 years and have tried to keep it pruned into a smaller tree form. Even when it was kept small, it produced hundreds of lemons every year.
I finally had someone cut it down since it was getting to be too much work for me to keep it under control. Even though it is getting no irrigation or any kind of care, it has grown back and has many baby trees growing near it. What can I do to get rid of this tree?
A: I w