How to stop "OS Services" from using tons of internet data?

[AC Question]

Hello. I used to use my mobile data 4G on my Android 7.0 and it was all fine. However, I finally got a router so now I use Wi-Fi connection. Since I started using Wi-Fi, something called "OS Services" is using waaay too much internet data causing me paying more fees to get extra data packages. It literally used 10.6 GB of internet data in a single day. It was not some Android update, I just don't know how that happened! I need it stopped by anyway or atleast to be able to put some data cap or something.