Locked out of Ipad and unknown apple ID

My 9 year old son received a brand new ipad 7th gen (wifi) for Christmas. The ipad was linked to my apply ID. He forgot his passcode and tried his most recent passcodes several times, to no avail, and was then locked out of his ipad. We had the ipad wiped so that we could reactivate the ipad, however the activation lock requires the apple ID/password that was originally used to set up the ipad (mine) however, it says the apple ID is b*****@gmail.com - this is not my apple ID! My son has now set up an apple ID with his gmail account, which does start with a "b", however we cannot login with this and I checked online and the device is not linked to this account. So we have no idea whose apple ID this is, so can't reset it, and can't log on! ANY suggestions would be most welcome! (Also, our nearest apple store is 3 hours away...)

Many thanks,

Michelle