Too much data been used to do the software update

[Gem2]

 I updated my Xperia m2 to lollypop a few days ago and ive just realised that my last contact bill was over a hundred pound ( but it is usually thirteen pound). I looked at my data usage and it said the software update app had used about 1GB of data even though I only have 250GB a month. I dont know why this is? 

Spoiler

[Hampus]

Hi,

I'm a bit confused, you say you have 250GB a month and the update used 1GB? If you update the phone OTA (direclty in your phone) via mobile data, this data will of course be used from your data plan. It's always suggested to use a Wi-Fi connection if you are going to download larger files and/or updates.