6.0.1 Marshmallow Update on Samsung Galaxy S5 - Now I have no Network
My Samsung Galaxy S5 phone let me know today that there was an update available. Great, right? But when I finished the update to 6.0.1, all of a sudden my AT&T network died on my phone. I have bars, and it says AT&T in the top left hand corner, but there is no 3G/4G/4G LTE sign anymore indicating I'm connected to the network. I can still send and receive text messages but not picture messages. Text messaging is all I can do with my phone now when I'm not connected to wifi. I can't use any apps like Facebook, Snapchat, YouTube, any that require the network if not connected to wifi. I have already tried the following troubleshooting items, so please do not suggest these:
1) Resetting the network settings
2) Rebooting the phone
3) Removing the battery for a few minutes then rebooting
4) Turning off the phone, removing the SIM card, turning the phone back on then back off again, replacing the SIM card, and turning the phone back on again
5) Making sure data is still on
My tech friends all tell me it sounds like the update isn't compatible with my phone, so I'll need a new SIM card. Is this true? I use Straight Talk on the AT&T network. This isn't the first time that an "update" to my Samsung phone has either outright bricked my phone or made it nearly impossible to use because it severely broke it (last time it was the Galaxy S3 a few years ago; it entirely bricked, and I had to take it to a Samsung kiosk at Best Buy for them to do a hard reset to factory settings just so I could use it again. I lost everything because I wasn't able to back it up before the so-called "update".).
I would really appreciate any help I can get for this. Although this phone that I've had for less than two years has been giving me issues for a few months now even before this latest dump on it, I can't afford a new phone any time soon, so I'd prefer to get a fix for it rather than shell out hundreds of dollars for a new phone. Thank you!
P.S. I've attached a screenshot of my phone so you can see the top bar area where the 4G sign is missing meaning I'm not connected to the network, but I still have bars, and the AT&T sign is still there.