Unable to erase my iPhone as it shows error "Erase pending"

My iPhone battery got fried so I had to order a new phone. I'm doing a trade-in so I have to make sure that the phone I'm trading in is erased. Obviously I can't erase the phone on the phone so instead I did it on my MacBook through my iCloud account. The only issue is that it still says "erase pending" and says it will erase when the phone is connected to the internet. But my iPhone won't be connecting to the internet again because it's never gonna turn on again. What do I do?

[Re-Titled by Moderator]