Regarding the AT commands, things to check.
Check if you have set the ocieanconnect APN. (In the manual parts 0 and 1 below you will see a few examples)
Some devices need a reboot in order to make the APN persistent…
https://forum.iot.t-mobile.nl/category/9/starterkit
Scrambling, try to see if you can set it to FALSE…
Device registration, is the device visible in the devreg tool, maybe delete and reregister with the IMEI of the device?
http://devreg.iot.t-mobile.nl/login
Hope this helps…