Why is Software Updates on my iPhone using so much data?

This is happening on my son’s phone and every month is a battle with him with going over on data. So today I reset my cell usage stats, and in the 20 minutes I was out of the house and not on WI-FI, System Services / Software Update claims to have used 747 MB of cell data on my phone. We have since turned of all automatic updates on the phones, but everything I’ve read on here and macforums says that won’t work… we’re talking GBs of updates every month, per phone, at $12 per GB. I’ve been on iPhone since they first came out, but this is last straw territory and I’m a vindictive SOB with stuff like this. Meaning, it gets fixed or I never buy another Apple product ever again and thats just the first step. There is an action that multiple people who’ve all been wronged financially by the same entity can take.