It's frozen shut probably due to a bad icemaker seal or faulty inlet valve. Thawing the ice is the only way to remove it without damage. Once removed, follow the ice. Did it start forming at the bottom of the ice maker or above the icemaker at the fill tube? If ice is inside the fill tube replace the water inlet valve. If ice formed under the ice maker replace the icemaker. I usually replace both parts since they are water related and work together. No one likes a flooded kitchen.