This happened to my wife's iPhone 8 when she was still on Bell. She was downloading Netflix shows for our 4 year old for our trip, and it booted her off her WiFi while she slept and used up gigs of Data. Needless to say Bell refused to refund.
I would always buy a card for use when you arrive in the area you visit - some countries have areas that are better served buy one provider and may have poor service with another. They're always for sale at the airport when you land.
