Did you pull a permit, is one required in your area, what does the contract say because inspectors help by checking work for free. If I had a non performing , wrongly oversized AC that will now leave me more humid I would make the installer put in the right unit, I bet he didnt do a load calc in writing, which is to your benefit if you did have 2 ton before, You hired a crooked hack if he oversized you, as you state you cooled before with 2 ton.