Someone has used my number on WhatsApp without me knowing.

I have had my device for over a year, and when I inserted the SIM card, I received a large number of messages from numbers and groups I didn't know. I simply thought they were spam numbers and blocked or ignored them, but suddenly I saw that in these chats there were messages from me that I NEVER sent. Unfortunately, I don't have images because currently my number is blocked and I don't know why (I think it might be related to this), and no one in my house uses my phone or anything, and I am completely sure it's not them because my WhatsApp has a password and I am the only one who knows it.