What you were told was right Patsyann.
Weed killer will just run off those waxy leaves and kill off the desired plants.
If its on a paved area, skim it off with a shovel, spade or hoe, on grass, mow or strim it. Do this regularly and it will gradually give up the fight.
On vertical surfaces, cut through the stems and pull them up or down.
It can be a dirty job, so wear gloves and eye protection.