Barbarians spawning even though barbarians are turned off

Barbarians might spawn in your territory when your population is very unhappy. You can tell if your population is very unhappy by an angry looking happiness icon. THere are several other consequences from your population being unhappy:

When your happiness is negative and your happiness icon is looking angry, your population is "very unhappy." If your population is very unhappy, your cities stop growing altogether, you cannot build any Settlers, your military units get a nasty combat penalty, and rebel(barbarian) units may spawn inside of your territory.

Source: Civilization V wiki happiness section

You have so much unhappiness that you reached the Unrest(Very Unhappy) level. (and you've actually gone past the Unrest level) On this unhappiness level,barbarians will spawn on your territory,cities won't grow,and you can't build cities. Try to build buildings that provide happiness,acquire luxury resources,discover natural wonders,get a mercantile city-state to be your friend or ally,or,if you are desperate,you can starve your city until it reaches a smaller size (this will give you also many disadvantages) to reduce unhappiness until your citizens are merely unhappy (look for the unhappiness icon;if it looks sad,your people are unhappy,if a bit angry,your people is very unhappy. If even more angry they are very angry. Just increase your happiness until your people is happy or unhappy. Also,unhappiness provides,for each point of unhappiness,a penalty of 2% on gold,production,and combat.