Denoisers by nature blur things, which is how they remove the noise. We'd really need to see the render to comment - the thing about noise is you should give enough passes that the noise is not extreme, before letting the denoiser "tidy up the rest". Since you said previously it was "very noisy", then it is possible you hadn't let it run for enough passes. Share the image, and info like how many passes you rendered for, what the noise level was, and so on :)