Why is my service so bad on galaxy s5 active?

[AC Question]

I bought a new Samsung galaxy s5 active with AT&T. The first couple weeks, everything was fine. The phone worked perfect. Over the past month, I have started having horrible issues with service, no matter where I go. It will day I have 4g LTE, but my messages won't send and I can't make phone calls. I have to repeatedly resend texts and constantly redial to get it to go through. The Internet part is extremely slow at times and most of the time, won't even load. I haven't dropped the phone or anything like that. I'm not sure if I have a faulty phone or if it's something that I am doing or have done. I have done a factory reset twice and neither one did anything for it. The phone seems to work better with plain 4g service for some reason. Any suggestions would be great, even if it's go buy a new phone!

 

[B. Diddy]

Welcome to Android Central! Double-check your APN settings and make sure they're correct: Programming non-AT&T devices with the correct APN and MMS data settings- AT&T Wireless Support

It might be a bad SIM card--bring the phone back to AT&T and ask if you need a replacement card.

 

[Ljtank84]

B. Diddy, i did everything that you stated in your post. I checked and double checked both apn settings and Sim card. Both were fine. Do you have any other suggestions or is my phone a dud?

 

[B. Diddy]

Did you already talk to AT&T? I'd ask them either for a new SIM card to see if that works, or just ask for a replacement phone.

 

[Rukbat]

Ask your local store where the Device Support Center is. That's where you bring phones if they don't work. (And it's why I pay more for AT&T - their support is the best of the 4 carriers.)