unlimited talk and text, plenty of data, but frankly most of my data usage is via Wi-Fi at home so I suspect that doesn't count against my plan. I pay $60 per month for 2 lines on their 55 years or older plan.

... with a WiFi connection, which I didn't have (again) until recently.

It was an unlimited plan, but before the cable WiFi connection, I often got warnings of slower speeds upon using 30 GB of data for the month... long before the month was over.

This link provides tips to reduce cellular data usage:
https://www.reviews.org/mobile/how-to-reduce-data-usage/

It's possible that AT&T is being dishonest. I'd be really curious what would happen if you switched to airplane mode while not using your phone.

First uninstall any apps that you don't use. All phones come with "bloatware" preinstalled and impossible to delete but you can disable them, effectively putting them to sleep.

In settings should be a setting that lets you turn background data off or for that matter all data. If you can't find it go to an AT&T store and they will help you.

I've used Consumer Cingular in the past. If you're a senior it's dirt cheap. Unlimited talk/text and select a data plan. If you get close they notify you. If you go over they automatically bump you to the next level. You can re-set to the lower level at any time. That way if you're on vacation and using navigation a lot it's all taken care of until you get home and reset. They operate on the AT&T network. All for about $25/month.

Note: I'm currently on Verizon and will move to CC again as soon as my contract is up.

You will still be able to use your phone and text messaging.
I would absolutely dump AT&T and look for a plan with unlimited data. We used AT&T for years, and usually had unlimited data. They stopped for one contract period, but reinstated it later.
We were paying $225 for three lines.
We now have TMobile 55+ and pay $75 for 3 lines, unlimited data. Their coverage is a little spotty in some areas compared to AT&T, but overall, we are happy.

that ping your phone, location, etc. Anything that you accidentally have set to "allow all the time" rather than "allow only when app is open". I've been caught by that a few times, or forgetting to turn an open map app off.

We only get those messages when we're traveling. Myself, son, and daughter are all on our family AT&T plan. Hubby is on the one for work. Between playing games that use maps/location svcs, surfing the web, downloading, and triangulating between different map apps, we usually hit our max if we're out 10 days or more.

I jumped over to T-Mobil about 7 years ago from ATT, never looked back. Unlimited everything, and if you travel international coverage without having to purchase in advance the estimated minutes needed.

There are some costs on the international, but very low, and mostly by the partner company. So a .30 charge for unlimited texting when in Jordan (it was something like this), same for majority of European countries, with some being with out any (always less than $1.00), one time usage fee.

Its an option somewhere in your settings. Even if you are not browsing the web or such, your phone will use data to update apps, get notifications and so on.