I forgot to turn off the data button on my iPhone. Cost me $150.
Two different school principals had a worse experience than yours. One went to Mexico for a week. The data charges were over $1K. One went to China for a week. The data charges were over $2K. In the latter case, ATT comped it on a one-time basis. If it happens to you, and it’s the first time, plead ignorance and poverty, and you might get a break. The second time, you’re on your own.