How Do I Fix/Prevent This Network Change Problem?

[neo_n]

So my network (AT&T) has ben upgraded, and they sent a new phone, they sead that I will have to activate it and That my current phone won't be able to work other then 911 and 611. First I don't want to switch phones since the one I use has already ben optemised for me and has a bunch of installed apps and accounts linked. Going through personalizing everthing would be a pain to deal with. Also my phone is a good phone, I'm already using most of the internal storage(128gb max) and some of the sd storage for all my stuff, mostly it's games and downloaded videos. It's not the best phone but it's probably better in every other way.

I would prefer a work around this problem, such as the sim card, my current phone had a 4g sim card and the one they sent had 4g LTE. I did attempt to switch to the other sim card but got stuck when the proccess required me to get infomation I didn't know about, so I gave up around 11:00pm because I was tired. Also the new sim card has an unkown phone number when I checked. I wold like to resolve this as soon as possible so it doesn't become a problem later, but I don't know where to begin. My phone is the Blue G90 pro, and has 2 sim and 1 sd card slots.

This is the 2nd text message:
AT&T Free msg: Your new cell phone should've arrived by now. Let's activate it! Go to att.com/activatephone to set it up on our upgraded network. If you don't activate your new cell phone, we will automatically activate it in about 2 weeks. Once it's activated, your current cell phone will only be able to call 911 and 611 until Feb 2022. If you need assistance, visit an AT&T store or call 800.880.8581.

[Buenchico]

People here might struggle to help you because cell phone contracts, and indeed cell phone systems, seem to be very different in the USA than the ones that we have here in the UK. (We don't even call them 'cell phones'!)

You might not be able to do what you want though, as this Amazon USA page, advertising the Blu G90 Pro, specifically states "Not compatible with NEW AT&T or Cricket activations or with CDMA Networks like Verizon, Sprint, and Boost Mobile":
https://www.amazon.com/BLU-G90-Pro-Gaming-Smartphone/dp/B08C6XBCRT
(That's where things get confusing to anyone here in the UK. Where we are, all unlocked phones will work on any network, so your problem isn't one that people here will have encountered).

If you've got an AT&T store near to you, asking the staff there might be your best way forward: https://www.att.com/stores/