Data usage seems way higher then usual for month after 18.2 update.

It's not always the iOS update's fault!  Many things can cause phone problems.  If you tell people you think it's an iOS update, it might make it harder to fix or find a solution for the real issue.

Remember, the right question often leads to the solution!

iOS updates aim to enhance user experience, boost security, and fix bugs rather than disrupt core features. The majority of the issues after updates might stem from underlying, unmentioned factors. Updates won't typically alter personal data but may refine settings or features. Backup before major updates for safety. Review Apple's update details and backup advice for a smooth process.

Kindly consider checking your settings and addressing any device issues before attributing the issue to external factors. This could be a pure coincidence that the iOS update affected the iPhone functions.

Before initiating a standard iOS update, it's advisable to create a backup. Have you completed this step? If yes, proceed with the restoration from the backup.

See what each update does: About iOS 18 Updates, About iOS 17 Updates, About iOS 16 Updates, About iOS 15 Updates, About iOS 14 Updates, About iOS 13 Updates, About iOS 12 Updates, and so on...

I don't think the data shown is for a month. Ask your Carrier for the period-wise data usage. You are not charged for the data consumption based on what is disaplayed on your iPhone.

What is the Last Reset Date* on your device? [Scroll all the way to the bottom]

Starting this Date* there are two sections which provide data for you analysis.

Under Cellular / Mobile Data Section

Current Period and Current Roaming Period cellular data usage.

[Scroll Down]

Call Time section

Current Period and Lifetime Calls.

How did you assess for which period the data usage belongs to?

Just to clarify, it's important to understand that a single SIM card can actually be used across multiple devices. This means that you can consume data from any device, including Android devices.

All the data consumption associated with that SIM card is consolidated in one central location: your trusted carrier. It's worth noting that your carrier will bill you based on this consolidated information. Therefore, if you need a comprehensive breakdown of your usage, I would recommend reaching out to your carrier and requesting a detailed itemized bill.

By doing so, you'll have a clear overview of your usage across all the devices you've used with that SIM card, ensuring transparency and accuracy in your billing.

If you're using an Exchange ActiveSync account, it may continue to use mobile data even if you've turned it off for Mail and Calendar. To see the mobile data usage of your Exchange ActiveSync account, go to Settings > Mobile Data > System Services.