Yeah, I'm still scratching my head about this one. Thanks for your reply. I was only logged in, via the website (not app) on a brand new mobile phone (not my computer). I was in my home & didn't have Bluetooth enabled. 

The new SIM was popped out of a perforated card I'd just received from the phone company along with the phone (under a week ago.) 

I went out of messages & back in & there was another user's eBay account, complete with their email address & other info.