Villagers Spawn out of nowhere and multiply

Put the summary of the bug you're having here

What I expected to happen was...:
I spawned villagers to populate my town

What actually happened was...:
The villagers mass produced fast and now my town is crowded. I cleared the entire town but using /kill but they still spawn in certain places of my town

Steps to Reproduce:
1. Build a suitable town
2. Spawn some villagers

3. Watch them reproduce like bunnies