You could have a virus. Plus, I have heard of ppl hacking phones and making them record voice and take video of your surroundings while the phone was powered off then emailing this stuff to you. I think it was a 2o/2o episode about someone stalking a teenage girl. The family changed their phone numbers and account only to find it was still being hacked.
I think in your case, you have a broken button and it is calling the last person you called. My phone used to do that until I bought a flip phone where the buttons were protected.
=D>