Just tell her you don't use Whatsap... I don't either, this happened to me one time, just tell her you don't uses social media to communicate then tell her if she won't give her cell phone ask her how you are supposed to communicate. Make a joke about it... tell her you guys should get 'pagers' and hope you can find pay phones.... suggest 'smoke signals' She gave me her number, and then couldn't get her on a date... no problem.. I just moved on. The point is don't get all serious. joke about it, if she doesn't respond to humorous masculine behavior she's not interested. You can't make her give you her phone number, then even if she does, doesn't mean she will meet up with you. If she won't she has low interest or she's not a normal woman... either way; walk away.
Not to be accused of name dropping, but I know Brad Pitt, we meet during the "Make It Right" foundation about 10 years ago. He's not a friend per say, but I have spent time with him. The last time I spoke with him, he was asking questions about how NCOs might behave (since he knew I served in the Army) in a tank crew in preparation for a role where he portrayed a tank commander in WWII a few years back, I told him some stoies my grandfather told me, since Paw Paw served in WWII as a Sherman tank crewman during the war, and if you haven't seen the movie "Fury", I think he nailed it. You will never hear me say anything bad about him. He really is a decent guy, married to a complete lunatic, so in many ways he has a lot in common with many of us. This divorce cost him, like it costs all of us but he's fine. But he did sell his house in New Orleans so I haven't seen or heard from him in years.
I think there are a lot of lessons we can learn from mistakes he's made, his marriage to crazy town, his involvement with "Make it Right" which also turned into a sh!t show, not because of anything he did, but because that foundation hired an incompetent CEO. Wisdom comes from mistakes we make, embrace failure because failure makes us better people "That which does not kill you makes you stronger."