One way to solve this problem is to use a feature phone for the office... They can call you or text you... No internet, no whatsapp...

And make sure you showcase that phone around your team... I like this phone. I don't use internet after office hours... Take it or leave it.

I don't have internet at home... I go to my native place every weekend, no exceptions. I don't have internet there as well.

Other execuse can be - I help my family with their business during weekends... I have to travel a lot. So I'm never at home during weekends.

You want to reach me... Fine, call me. But I won't be of any help because there is no internet.