HELP! How do I re-attach dryer vent hose?

This may seem off subject but it's not really because it was while I was decluttering and cleaning my laundry room that the problem occurred. When I pulled the clothes dryer away from the wall to clean behind it, the vent hose detached from the dryer. Not a problem, I thought, just hook it back up. Little did I know. When I squeezed my way back there, I found that the darn thing didn't fit. Obviously, it fit before, only when I tried to fit the tin-looking elbow thingy at the end of the hose, it's diameter was too large to fit inside the dryer vent casing (or whatever it's called), and too small to go around it. I've tried stretching it; I've tried compressing it; nothing works. This absolutely makes no sense to me. I know there must be an easy solution but I sure can't figure out what it might be. Thanks....