Can't initiate MMI Codes

so i have the note 4 on at&t, and what im trying to do is make my phone ring longer by dialing *#61# to get info, and then using **61*1xxxyyyzzzz*11*XX# (xxxyyyzzzz=phone number; XX=ring duration by seconds/max 30) to set the duration of phone rings. but every time i try to send mmi codes, it always returns with "CommDiv Fetch Failed(408) - Retry Again/Later" i even tried using **61*11**30# and it brings back "CommDiv Divert All Users EnbWithTar Failed(408) -Retry Again/Later"

again all im trying to do is make my phone ring longer. and im using the note 4 on at&t (n910a).