Wait, what do you need Snapchat for on a Punting phone?
But easiest/cheapest option is to just get another sim. Most phones these days are dual sim capable. Where the SD card goes, you can actually put another sim.
Some new options will appear on your phone. When you make a phone call, you can choose whether you want to dial with Sim 1 or Sim 2. You can also disable either sim from the settings menu.
So if you're not punting and a WG calls you, as long as Sim 2 is disabled, the phone won't ring.
For WhatsApp, you can just download WhatsApp business which is literally the exact same thing as WhatsApp and made by the same people. You can assign Sim 2 to that. As far as I can tell, the only difference is that for the recipient, it will say "This chat is with a business account" right at the top.