I am certain my ex-husband has access to my phone thru his. How can i prove it.

[PaulaRose]

I recently broke my phone and my ex husband hands me the exact same phone and says that he paid to have it fixed. OK,now when I say my phone was broken I mean demolished!!!! Now why would anyone go and pay over 50.00 to fix a fubarred phone when you can get a brand new one at Walmart for 40.00. He knows this cause he bought me the 1st one. All my settings keep getting changed, messages I didn't send are being sent, messages I haven't read yet are shown as read. I log out on facebook and what do y'all know.... When I go to get on next I'm already logged in
I have factory reset my phone a couple times but it is still happening. But my phone has mysteriously dissappered for a couple times and guess who finds it each time...yup, my ex husband.. How do I prove that he has access to my phone thru his phone.