Default No mobile 3G/4G

Just got this phone today was on the phone with att for over an hour. They had me make sure the mobile data was on then we add new access point information and still nothing. I can get on wifi. I have tired everything I know to do. Also very so often I the info bar instead of the AT&T logo there is just some numbers 074723 not sure if this might help anything help with this would be appreciated.