Activation / Stuck on "Searching"

I just replaced the SIM card on my iPhone 7 because the previous one stopped working. I was stuck on "searching" and was told at the T-Mobile store to reset my phone. I backed it up and subsequently did so. However, the phone remains stuck and unable to be activated on iTunes because "the activation information could not be obtained from the device". I made sure that the SIM card was inserted and tried again, but to no avail.

Any help would be greatly appreciated.