Minecraft – Why is the Iron Farm not working

Because you accidentally attacked a villager or two, your popularity in the village is probably low enough that the Iron Golems will attack you on sight.

One option is to prevent more Iron Golems from spawning, and then killing any remaining ones aggressive towards you in the village. You should theoretically be able to prevent them from spawning by either reducing the village population to fewer than ten villagers, or by reducing the number of homes (a home can be removed by deleting the wooden door—the structure itself does not need to be demolished) to fewer than 21.

Once you have prevented the Golems from spawning, you can attempt to increase your popularity with the villagers, to prevent any golems that spawn in the future—because of population increase/home construction—from being hostile. The only way I know of to increase popularity with villagers is to trade with them, specifically for their last item (related Arqade question).

Another option, if you don't care about the village at all, is to wipe out the village's population, resetting your popularity for that village.

Disclaimer: I have not tried the aforementioned solutions myself, so I cannot guarantee they will work.

There are two sides of this coin either you don't have enough villagers/village is not large enough OR you just need to move your farm to the top where it would be more likely. There is the long hard way for the golem finding a cave and mining until you have enough.