They even suggest to drink it after feeding, to minimize the effect on passing it on to the baby.
Coffee also drives water out of you body, that's probably another reason you do not have enough milk.
You need twice as much water when you breast feed, that's 4000ml. You need to drink a lot of water, plain water, no tea, no coffee, no squash, no juice, plain water.
You need to improve your knowledge on breast-feeding. Go to learn.