You may have a problem with the parking/emergency brake, which is a small drum brake inside the hub portion of the rear rotor. Loosen the adjustment on the emergency brake to release them.
You don't have the parking/emergency brake on, do you?
OK, it sounds like you're 'over your head' on this repair, you need to find a friend/acquaintance who knows brakes to help you. These are critical to your safety, I can't diagnose this long distance.