“0$ to get started, then pay as you go” reads to me: “0$ to get started, and then you can order add-ons and extra features as you need them”, not “$0 to get started, but we may start charging you virtually unlimited amounts at any point without prior notice”.
When signing up for the “Starter” tier initially, I completely misunderstood this. I didn’t have to enter any credit card or invoice details, so I thought as long as you don’t have that info from me, you can’t and won’t bill anything.