Late to the chat but from what I can read, every Smarty forum regular seem to be advocating for checking our phone settings again and again when everyone says nothing has changed from their previous provider.
I've just purchased a £15gb data only sim for my campervan, pretty much only used it for google maps between 2 and 4 hours a day and a couple of youtube videos, and I've ran out in 4 days! I repeat, 4 DAYS. 15gb! For comparaison, I reset my stats on my iphone to check my vodafone usage, in one day of almost 6 hours on my phone, 3h47 on maps, 35mins on youtube, having Polarsteps set to always allow tracking my location, hotspotting to my laptop for another hour of youtube, plus all the other background stuff etc.. it used 1.9gb
Personally, I think it makes no sense. I don't see why it would somehow use that much more just because it's casting it to my phone over wifi rather than being directly in it. I'm probably just going to get a refund and pay a bit more money but for something that actually works, especially since the chat support wasn't very helpful..