Can't restore original iPhone on iOS 3.1.3

I have been having issues restoring the original iPhone on iOS 3.1.3 to do a comparison of that iPhone with the new iPhone 14 Pro Max.

When asked to connect to iTunes (even after I added the SIM card), the original iPhone still does not recognise the Cingular SIM Card, and after I connect to iTunes, it stated:

We're sorry, we are unable to continue with your activation at this time.

Please try again later, or contact customer support.

Then I tried to put the iPhone on DFU mode to reset the phone, but then it stated "The phone used to be on DFU mode, but now it is no longer in DFU mode. Please disconnect and reconnect it to DFU before restoring" even though the phone is clearly in DFU mode.

I really need help on what to do. This phone is just unrestorable.

I tried to restore the phone to make it a fresh slate to be able to make a YouTube video since there are some old information on the original iPhone I don't want to see (I bought the phone 4 years ago to replace another original iPhone however, so it is basically erasing my old data from a long time ago)