iPhone 6s stolen and erase iPhone pending. How can I know erase has been completed ?

Hi there !

My iPhone was stolen from my home yesterday (while I was in another room !!!), and I traced it a couple of blocks away half an hour later via Find my Phone app.

Although the phone is protected with a 6 digit password and fingerprint, two calls were made to family members from the phone during the time I was searching from it, which means that who stole it had access before it automatically turned of (it locks in a minute). Even this seems impossible and I don't know how to explain it.

By the time I could realise that the phone is not misplaced at home, I connected in my iCloud on my laptop, chose the lost mode (it was still connected and I could see it a few blocks away from here) and then I chose to erase my iPhone.

As soon as I pressed the erase my iPhone, the erase command appeared pending and the old location is "stuck" on iCloud which means that I can no longer spot the phone. Almost a day went by and I only see the old location and the pending erase command. I don't care about the phone, but I want to make sure that my personal data is no longer in it. Needless to say that iCloud password was reset together with any other password I could think of.

Because I have immediately canceled by mobile number to avoid frudulent calls, I am not sure if the erase command is still on, if it will work when the thieves just reopen the phone (without doing anything else) or if it will work only if they connect to wi-fi. I have searched on various forums but posts were either too old or too unclear.

My outmost concern is how I can make sure that everything has been erased under those crazy circumstances.

Thank you for your help in advance