Hi Filip,
If you responded right away, your respond rate should be 100 %, I think it only takes some time till Airbnb updates your response rate...or it will be updated after few more inquiries, not sure... Anyway, make sure to respond quickly and you'll definitely have 100%. 😉
For me, the best way to respond is via the Airbnb app or online on your computer on the Airbnb website. I think the app is even better cause it's very easy and quick. The sms and email are just some kind of notifications about the inquiry, don't respond to them, just use the app.
Hope I could help you a bit. Happy hosting 🙂