If your Armor shows on your Hero but isn't equipped in the 'Armor bonus' tab, you won't be getting any bonuses.
Once you have purchased some new Armor, be sure to equip it by selecting your Hero from the World Map then Armor Bonus to correctly equip the Armor to give you the bonuses. If you weren't getting the bonus previously this is because the Armor is likely only being worn in the "Appearance" tab but is not selected for Armor bonus.
Armor Bonus vs Appearance
Here, Cyrup is wearing the Phoenix Armor in the Appearance tab. This shows up whenever another player looks at Cyrup's profile or when viewing Cyrup's Hero. The Celestial Armor can also be equipped in the Armor Bonus tab for the extra bonuses in battle, but it doesn't need to be worn.