Can another person hack my iPhone number?

I have 2 lines the other being my spouse. Let us just say, for brevity, I have monitored our usage. At a point there were calls listed on my phone usage and text messages to this person that I did not make nor would I make. There were other calls using my contacts I.e. my dog groomer, a half day of texting. Just crazy! AT&T told me if a call or text showed then it was made from my phone…..did he have access to my phone, probably!