Given it's a new phone but old SIM card, are you sure that the SIM is actually working with your current phone? Can you send and receive phone calls like you used to, or is it a matter where phone calling is working but text messaging is not? If you can't do either, perhaps you need to log into your account on your cellular service web site, and check its status. Since your SIM card is how your phone authenticates itself to your cellular service, if your carrier ties your account to a particular device you might need to just update your current status (your new Moto G Stylus). You 'might' need to also update/edit the APN settings in your Moto with that SIM card, typically that info/data is retained within the SIM but since you apparently pulled the card from your previous Moto G7 and put it into your current Moto G Stylus, that might involve editing the APN settings. Your carrier will most likely have the necessary APN data on its site.