Ignition barrel release

Hi, our ignition barrel had to be released by a call out man to get the car started. Some nib had sheared of due to turning the ignition key whilst the steering wheel was still in lock. Anyway we asked the call out man to show us how he released it so we could replace the tumber ourselves. My husband is fairly handy with cars so he was confident that he could release the barrel himself and replace with new/secondhand barrel. He hasn't been able to release it though, he has tried for hours. A friend as an Zafira ready to be scrapped and my husband asked if he could try to release his barrel to see if he doing it correctly. Hey presto the barrel came out instantly. Can anyone suggest why ours isn't releasing please.