Vodacom will sometimes lock their dongles to only their SIM cards,meaning you cannot use MTN ones on them.
There is a software update you can install on it to allow it to use an MTN simcard with our APN on it if you sign up with us and port your number.
The risk is that if you install the software it may break your device and it is usually not possible to to rollback the update. This is a risk you would have to decide on and be responsible for.
I trust this helps.