Claiming warranty, I read the guidelines, but should I still be worried?

Hi everyone,

I was wondering if anyone out there had any thoughts on this.  I bought a new Galaxy S9 a few months ago, and it appears that many people are unable to receive my text messages when I include a picture.  I talked to the AT&T rep via online chat, he did some troubleshooting and couldn't find a fix.  So he said he would be happy to claim my warranty for me and send a replacement.

He sent me the link with the warranty guidelines, which I read, and he had me confirm.  My replacement phone came in the mail today, but before I even open it...here is my question-

Since the problem with my phone does not appear to be physical, and the rep could not figure out what was causing the issue...do you think I will be surprised with a huge replacement fee on my bill if they receive my old phone and can't figure out what was causing the problem?

I've had some issues before with AT&T being kind of shady.  I'm not generally a paranoid person, I just don't want to get burned again.  I saved my chat transcript, and the AT&T rep made it sound like "oh yeah, claim your warranty, it's free and you're still covered, no problem," but I'm a little concerned.

I know you can't predict the future, but does anyone with insight have any thoughts? 

Thanks for any response.