While we were together my ex boyfriend had my admin password for router. It was set to default settings as I had no clue about any of this kinda stuff. I have since factory reset my router and changed admin and WiFi password, but he is still able to access it, as I noticed and screenshotted an unknown device. How is he doing this and what can I do about it?
You could set up a MAC address filtering on your router and whitelist only devices you know and you are using. The cons of it is that if any of your guest will want to use your wifi you will have to add his mac address first.