Hi,
Is there any other Spark NZ SIM you could try on RUTX11?
Also, it could be that operator is blocking you from using that SIM on the modem inside RUTX11, is there any chance you could get information on what do they see from their side? As it registers to operator successfully, there must be something that doesn't let the data connection go through (considered that you really used the right APN's).
EB.