Followed Instructions..Laundry Day still not working

Have you also looked at the alternative instructions ?
https://games4theworld.forumotion.com/t32978-alternative-manual-for-downloading-and-installing-the-sims-4#

Installed in that order ?
Not skipped a DLC ?
Extracted with WINRAR ?

I use 7zip and everything but that one and the last part of the instructions works

I have the same problem but I now realised that there is a separate dowload for My Pet Stuff...

Do I need to reinstall the entire game? 

This is what worked for me: I restored my computer to an earlier time and then installed My First Pet stuff and new Update in the correct order and game works fine now:)