Cant locate my nem

so i transferred my XEM from the exchange site to my nem phone app. so when you received your XEM on the app this popup thing comes up almost like chat box. saying unconfirmed XEM coming in. Silly me thinking that i had to press the amount and the msg to match in order to CONFIRM the transaction. so i pressed send and went away my XEM to somewhere in that chat box thingy. I panic and i thought maybe i should try again so i did the exact thing and ended sending away more XEM. wasnt sure what to do next. but i notice the address above on the chat box thingy so i copied it… i went to created another account using that address. it somehow worked, i found some XEM on it but the numbers didnt match with what i transferred. the date also didn’t match. i have no idea whats going on.
anyways i was wondering how can i get back my XEM and how was i able to access some random account. its not even mine. so if i had a nem address i can just go “add account” press " add key" put the address in and i can access peoples account and if i wanted i could steal their XEM. doesn’t seem very secure. OR maybe i misunderstood something. please explain.

i have attach some files. you will see what i mean.
image 1 is showing that i got my nem from the exchange web. that in the chat box thingy it was unconfirmed and i thought to confirm it i had to press the amount repeat the msg. so i did just that and phew it went away instead of getting it.
2nd image i tried again (stupid me) i did the exact same thing and another 5000+ went away.
3rd image is when i copied the address that given above of that chat box thingy and opened another account and i found some XEM on it but it didnt seem to be mine as the date was incorrect and the amount in it was also not matching. so i guess i accidentally went into some elsees account. should that even be possible? and where did my XEM go. because i pressed send. it was in that chat box thingy that popped up and the address was of that i copied from that chat box thingy so technically it should be there but its not. the amount that is it that address isnt the amount i sent and the date was in April or something. i never started buying XEM or downloaded the app until 2 weeks ago. so for sure it wasnt mine.