Att LG G550 cell phone problem need help?

I got a new unlocked Att LG G550 cell phone over the holidays, I use the Straight Talk Service so I also got a new Straight Talk Sim card.

I was able to get the phone service and number transferred and working fine.

However to use the extra's you must update the APN to the proper settings which I did but still no luck,

I Even went to Walmart and they tried still new luck, his answer was you may just need to buy another phone.

Any Body have any idea's??