There are messages on my phone I didn’t send and I am freaked out

This has been going on for three years. There will be messages on my phone that I know I didn’t send. They are always specifically to people that I used to date, and they never seem malicious. It is really creepy, and making me question my own sanity. I took it to the Apple Store and they couldn’t find anything. Is it possible someone who is obsessed with me has hacked my phone and is sending these and Apple isn’t picking up on it? I am genuinely begging for help. This is freaking me out and I feel like my privacy is being invaded, and I don’t understand why someone would send these messages.