Oxalis cannot be got rid of by pulling it up. Attached to the roots are dozens of little white bulbs, (have a look next time you pull some up), as you pull the plant, many of these drop off and grow into new plants. Oxalis needs to be poisoned, with repeat poisonings each year until there are no more bulbs left in the ground to grow. Or just live with it.
Hi! I know you hate having to type in the words as much as I do, but I am being furiously spammed, so I've had to reactivate that feature. If you're a real person I'd love to hear from you :-)