I remember my mom tried all those enzymatic cleaners, and not a one worked - but then, it had gone past the carpet, into the pad (it usually does), onto the slab, and up into the wallboard. She had to have a major remodeling (or reconstruction, actually). Fortunately, it was restricted to one wall of the living room.

I moved into a house with old pet stains, and again, the enzymatic cleaners were useless. But then, I was trying to get rid of old spots.

I don't have the problem now but I've heard vinegar is very effective. Whatever you do, DON'T use ammonia, because cat urine has ammonia it it. You'll just be inviting them back!