One of two things has likely happened. The locking pin has bent and is not retracting fully when the button is pushed. Or one of the mounting rings has come loose and bent, causing it to bind when turned.
Neither is an easy/pretty fix, and will likely require replacement parts after they have been separated (by force or cutting).
If it is only moving very little it is probably the locking pin; and you might be able to get it to retract by turning the lens back and forth while simultaneously pressing the release button very firmly. Even if you do get the pin to retract and release the lens, it probably won't return and function normally afterwards.
I would expect a loose/bent mounting ring to be warranty repair; but it wouldn't surprise me if a bent locking pin isn't. Either way, it's almost certainly best to let a shop do the work.