If you use Netlify in the free tier you cannot automatically go to pro tier either. Yet they will charge you for bandwidth > 100GB, and THERE IS NO WAY FOR YOU TO SWITCH THAT OFF, even in the free tier.
"Should be fine" is exactly what is not the case here. Better check your Vercel terms again.
From every Vercel document that I can read though is that when you exceed the limits of free tier they are just locked for 30 days unless you upgrade to Pro.
So unless I am mistaken this cannot happen on Vercel.
"Should be fine" is exactly what is not the case here. Better check your Vercel terms again.