Cat Spraying in Basement

Hello! TIA for any help and answers. I have two male cats that are just over a year old. After we came home from vacation this summer we found the basement stinking and they (or maybe it was just one of them) had messed in the basement multiple times. I had a friend come clean the litter box more than once a day, so I know it had to be because they weren't fixed yet. Anyway, we cleaned up everything we saw but whenever the heat pump kicks on and air starts coming through the vents the smell is very loud on our first floor and is honestly just unpleasant. I purchased a black light and found nothing but the smell is still there. Can anyone tell me what I should do or what products I could use? I plan on just washing the walls in the entire basement, but the floor is concrete and I fear that it soaked into the concrete and now I'm just screwed. Is that possible? I appreciate any help. Thanks!

Are they fixed yet? If not, no point in going all out in cleaning it!

Anyway, get a lawn sprayer and a few gallons of white vinegar. Give the entire basement a good spraying with the vinegar (I'm assuming it's an unfinished basement and can take some moisture, if it's finished be more careful). Yes it will smell vinegar-y for a while but once it's dry you shouldn't be able to smell anything. If you find where the smelly spot is, put some baking soda on it, let it soak up the smell overnight (or longer) then sweep it up. You might have to do that a few times. Also change your furnace filter because it might have absorbed the odor.

Yes they have been fixed. We had just adopted them and got the appointment set up for when we got home from vacation because I didn't want to leave them at home alone right after the surgery. Anyway I didn't think about the filters so that's a great idea in addition to everything else. Thank you for your help!

@kelseyy

You can use an exhaust fan to have the air in the basement sucked out and leave it running 24/7 and it also will draw out moisture and smell. Get quite a bit of activated carbon and spread it all around out of the cats reach. Have the activated carbon changed regularly till smell has died down. Or get a good electric dehumidifier. You can run all these three at the same time.
Get the air circulated and a good exchange of air is good.