New Iphone 12 Pro and new SIM card

We can definitely help you activate your new SIM card, @davidcarlsson. 

Thanks for your recent upgrade to the iPhone 12 Pro. Please power your device off, replace the original SIM card, and power it back up.

Once you have go to http://sm.att.com/eced0b31 and follow the prompts to finish up. Once activated please make a test call and follow back up to let us know its working.

We'll be standing by.

Keny, AT&T Community Specialist

I am having the same issue!

Purchased an iphone 12PRO Max via apple.com and ATT has sent 2 5G sim cards to make the phone work but I cannot activate via  http://sm.att.com/eced0b31 and ATT support online HELP can't activate the sim card either!
They (ATT) keep stating the same thing:  these sim cards have been activated to another phone.

Why does ATT keep sending me sim cards activated for another phone?

I am waiting for 3RD SIM CARD from ATT, I am just about done with ATT. Thinking of moving my phone to new service.

So many issues with ATT!

RAW59,

I am having the same trouble. It's completely absurd. I feel like I've gone through the Looking Glass. I've been on the phone with them for an hour now, going on my 4th person who can "help," but NO ONE can activate it. It pairs well with the unrealness of 2020, though. I think Trump must own AT&T.

I WANT TO GIVE YOU $100 A MONTH, AT&T. Why won't you help me become a customer?

I, too, have had two completely unknown-to-me numbers noted on communication from AT&T. They're like: Use the PIN code sent to 215-xxx-xxxx. Nope. Not my number, not my area code. I truly do not understand. The second I get my $250 VISA card--IF I am ever able to activate this (Edited per community guidelines)ing SIM card--I am leaving AT&T.

@ FLUKTTA,

So it must be that ATT is NOT READY for the 5G mobile devices? LOL!

Guess what else ATT is doing to me right now? I moved to a new EMPTY home and they state that an active account is linked to this address and they CANNOT give me internet service! As I told them, this is a BRAND NEW HOUSE NOONE has resided in it, they say Sorry, we can't move your account to the new home until you resolve the existing account: I told them but NO ONE has ever lived at this home it was a plot of dirt before I purchased the home.

Spectrum is going to get my phone and internet real soon if they don't get at least get my new phone fixed,at least I can use the internet on my phone but the house internet service is unbelievable!

ATT how are you going to compensate ME?????

So I transferred from Sprint and the activation claims to have worked but it did not.  Great. So now I have no phone.