Perhaps too late to matter, but.. I don't think you can reuse a Tello GSM SIM. (For that matter, I don't think you can reuse a SIM on any T-Mobile MVNO, once deactivated. I think T-Mobile Postpaid/Prepaid might be able to do it.)
T-Mobile postpaid SIM has a 45 days grace period to be reactivated with the original number, in case someone switches from physical SIM to eSIM and changes mind later or phone is broken. You can not reactivate the SIM with a new number.