It could possibly be soaked into the wood subfloor. It could be under the new carpet...

Who put down the new carpet and painted, you or the seller? Did you smell “cat” during your visits as a potential buyer?

I'm a renter and there was no cat smell when I went for the viewing. The work was done before I moved in

The first poster may be right, unfortunately. The cat urine may have permeated the subfloor. You may have to pull up the new carpet. Try Nature's Miracle spray. I have 3 cats who were always great about using the litter box. When we moved into a new home, my 16 yr old kitty was apparently protesting the move or marking her new territory on our new master bedroom carpet. I used the Nature's Miracle and it really did work. My cat was bad about 4 times then it stopped, thank goodness. I guess maybe she got used to her new environment.

I wish you luck with the smell and new place!

I would immediately bring this to the attention of the landlord. He probably replaced the carpet due to cat odor/pee without properly treating the subfloor that the pee soaked into.