…and turn the damn SIM off the second you clock out.
The number of people complaining here about being approached by their boss on their day off is too damn high. If you turn that SIM off via your settings, you won't be getting any notifications about calls or SMS. On Android (don't know about IOS) you'll even get a second whatsapp dedicated to the second phone number which you can use to communicate during worktime, and simply turn off the notifications outside worktime. I've been doing this for years and it is by far the best way to maintain a proper life-work balance. You can't feel annoyed/frustrated/tempted/guilty about not answering a text/call if you don't know it was there.
Honestly, do this before you start a new job so they don't know your old number. It'll make things much, much better.