System services using 12 times the cellular data I used to use since ios15

ive has extremely high cellular data usage in the last 4 months. Ex- in the last 8 years I only exceeded 2gb on 2 occasions. .09-1.3gb /month 90% of bills. Suddenly I’m getting 1gb in a day. The speed drastically reduces once it gets to 1gb- by the end of the billing cycle, my phone is so slow it reads as not having cellular service available. That’s 1 day into the month. Not good. I check my phone and 99% if the cellular data used is “system services.” I don’t have CarPlay and I don’t use Bluetooth. I turn it off always- I have a blue tooth microphone for my kids Ill play music on and I’ve used a hand free Bluetooth earbud sometimes- which I stopped for a month. How do I have blue tooth turned off and the Bluetooth services in my system services is using ½ gig a day? What is it? If my phone has speeds reduced to 1mb/s the more data that’s used- and it starts reducing at 1gb and decreases to non-functional at 5gb… my phone doesn’t work 75% of the time. This is a major issue. It appears A LOT of people are having cellular data increases on apple devices that are unexplainable- can someone help????