It could be that somehow APN might have changed or isn't parsed as it should.
What I would suggest is reset the device without keeping the settings with SMS utility text restore.
This way you will put your device into reset procedure and once it's done we can be sure there's nothing else that could be wrong with the device, so only APN set-up is left.
Then what we should do is send uci commands through sms utility. Please let me know how it goes.
<adminPassword> uci set simcard.sim1.auto_apn='0'
<adminPassword> uci set simcard.sim1.force_apn='-1'
<adminPassword> uci set simcard.sim1.apn='bangapro'
<adminPassword> uci commit