ASUS RT AC1900 Router w Netgear M1 issues

[wouterv]

I am not sure what subscription you have for the SIM card, usually there is a data bundle (x GB / month) and a call bundle (y min's / month). "unlimitted" data is usually not really unlimitted but shall be within some average bandwidth as described in the contract.
What happens if you exceed the data bundle depends on what is written in the contract, it can be that they put data on hold until the next period starts.
It can also be that they detected you are using the SIM card in a network setup and see data requests of many MAC addresses of the clients in your network, this usage can exceed the contract and have caused the termination (usually they sell dedicated data SIM cards with a different contract for this purpose).
The IMEI number is bound to the Nighthawk M1, SIM cards use different ID's.

 

[sfx2000]

The 3G/4G/5G TTL mangling loophole may be closing as the carriers upgrade their core networks to support 5G-SA...

The bandwidth cap management is handled by the Policy Control frameworks (PCEF/PCRF)...

And as previously mentioned, the IMEI defines the device itself (and type of device) - the SIM card (specifically the USIM app on the card) contains the IMSI (4G, 5G-NSA) and URI (for 5G-SA on some carriers) - that relates back to the user account and rate/comm plan provisioning in the billing system.

TTL mangling to bypass BW caps (or to allow tethering) is seen as toll-fraud by the carriers, so it's only a matter of time before that loophole gets closed.