Can't send text or mms messages on Galaxy Note 4 after upgrade to Marshmallow

[AC Question]

I bought a Note 4 Verizon phone that was unlocked for GSM for my Consumer Cellular account. I originally set it up and had it working for text and mms messages using the GSM settings for AT&T. Then I upgraded to Marshmallow using Kies 3. I had backed up the phone on Kies so I opened it up after the upgrade and got a message that the phone was locked and I had to sign in with a password on the phone. There is NO password on the phone.

I have the phone set to use LTE/GSM/UMTS and it shows AT&T as the network. I have set up APNs for both AT&T and LTE and have tried every setting on this forum with no luck. When I attempt to send a message to my email address, I immediately receive an error that I have to use a 10 digit number. I have sent a text from my email to my phone, but it wants to download the message and never does.

I think the upgrade messed something up in my phone. I attempted to use *#06# to get my IMEI and receive an error that it's an invalid code. I can make and receive phone calls.

Three years ago when I got my Galaxy Note 3, this forum got me all set when Consumer Cellular couldn't. Can someone please help me now?

 

[Darlag2]

I found settings that will work by checking all of the messages. It's LTE settings but using Cingular rather than att.

APN: att.mvno
Proxy: 66.209.11.32
Port: 80
User name Not set
Password Not set
Server Not set
MMSC: http://mmsc.cingular.com
MMS proxy: 66.209.11.32
MMS port: 80
MCC: 310
MNC: 410
Authentication type: PAP
APN type: default,mms,supl
APN protocol IPv4
Enable/disable APN green checked (enable)
Bearer unspecified

I also found that it only works when I show as connected to AT&T network and 4G. Unfortunately, the phone will start out showing 4G then switch to 3G. Restarting resets it but just for a short while. I have to figure out how to keep it at 4G, but at least it's working now.

 

[Darlag2]

So the way to sent text and pictures worked once then stopped again. I'm back to using my Note 3. I've been trying to figure out how to go back to 5.1.1 on the Note 4 but haven't found a good way to do it on a verizon phone, so it will sit for a while until I decided to try again.