Help Mobile network not available on unlocked Active

[Papote13]

I purchased a "new" unlocked Samsung Galaxy S4 Active SGH-I537 phone on EBay. Everything works fine except when I use the phone with my local carrier SIM card. When I insert the SIM card and turn on my phone, the carrier name appears and I get full bars. I can make a call or two, but then the carrier name is gone and no bars. At times I get the message: "Mobile network not available". I can’t make any more calls and if I try to the whole phone freezes and I have to do a hard reset. I’ve tested the SIM card on my old phone and it works perfectly. I have checked and the frequencies are the same for my local carrier and AT&T's.

I would appreciate any help on this matter.
Thanks.

 

[Rukbat]

Without having the phone to diagnose, I'd guess that you have a defective phone. (And I'd further guess that the seller was having the same problem, which is why he sold it.) If you can't get a refund, shipping reimbursed both ways, get a repair estimate. It could be something as simple as a bad SIM socket, which is cheap to fix.