Hi JF7162,
It's great to hear that you've treated yourself to a new iPad, we're sure you'll enjoy it.
As you mentioned this was to replace your previous pay monthly iPad, did you have a SIM card with it?
If so then we would have done an "upgrade" meaning a new device and possibly a new package, but this would still be linked to the same SIM card, therefore you should be able to place this into the iPad.
If this wasn't the case do let us know and we'll be able to take a closer look via a personal message.
Thanks
Emma_C - Forum Team