AT&T sent llc u304aa phone which I declined to get

what phones are you using?  If they are not on the approved list then they will stop working.

At&t is sending out free, cheap phones to replace phones not capable of Voice over LTE. The radiant core is certainly one of the cheap one.  My neighbor got the cingular flip.  

Unless you see 'VoLTE' in your notification bar, your phone needs to be replaced. 

If it drops to H or H+ during calls, it's not VoLTE, and is a 3G phone on AT&T .

    AT&T '4G' is HSPA+ or 3g service, and will be shutting down.

Important thing is AT&T sent phone which I refused to take and made me take time to go to post office to return, since if I don't return it in 14 days, AT&T charges for this garbage phone.  I'm sure many users have same experience. The way of sales of AT&T is fraudulence.

if I don't return it in 14 days, AT&T charges for this garbage phone. 

They are sending you a free phone. They aren’t going to charge you for it whether you return it or not and you don’t have to use it.

For sure, I talked to customer service. Over 14 days will be charged was the comment of the guy.  I will go after the manager who authorized this pre-fraudulent sales. Well -known companies in united states educate employees not to do anything fraudulent actions to customers but AT&T is different because that ruin their reputation. 

🤦🏼‍♀️. No.  Again, no.  You were sent this phone's because your current phones are not capable of working on AT&T network when 3-g shuts down. These phones are free. You are not being charged for them.  No contract.  No charge.  Zip.  Zero.

The person you spoke with on the phone was not aware that you were sent these phones as free Replacements because your current phones will not work on AT&T.

Let's put this a different way. Did you pay anything for these phones up front? AT&T has to charge sales tax upfront even on free phones. If you paid nothing upfront, no charge on your credit card, then these are free phones. If you would post whatever phone you are using currently we may be able to confirm whether or not your current phones will work on AT&T voice o er LTE service.  (At&t seems to think not)

Now I'm using Pixel 5. Even if 3G network becomes out of service, it doesn't matter. And I didn't pay sales tax because I didn't buy those phones.

At&at sent free phones when they shut down their 2G network.