A bit odd, because the US is specifically the one country that definitely has an area code that's mostly reserved from civilian usage, i.e. 555. Although not all numbers in it are reserved, afaiu they aren't given to randos anyway, and the store's spam system could be set up to never text or call these numbers.

I once looked up if there are numbers that I could safely use for testing purposes in my country, and we only have numbers from old popular songs, which curiously were also later referenced in tv shows. But it's a toss-up as to whether they're definitely unregistered in any particular area code. I'll probably have to use ‘+1555...’ instead.