How do I stop others using my printer?

[Danni1985]

I set up my envy 5010 printer just after the new year. I woke this morning to an email saying I’d used up all my pages. Turns out, my upstairs neighbours have managed to connect to my printer and they’ve printed documents! I’ve been trying all morning to get through to a person, I’ve tried changing the name of the printer so they see it’s mine and not their one, but how can I secure it more? How do I password protect it so they can’t connect? 

[Valsimot]

Are you using the same wireless network? The printer is secured in the same level wireless network is secured.

You can turn your printer OFF when you are not using it. No one can print if the printer is OFF.

[Danni1985]

I’m connected to my WiFi and I assume they have their own as my WiFi is password protected but the printer is not. 
I just need to know how to add a password from an iPhone 

[Valsimot]

Someone has your wi-fi password and has access to your wireless and your printer. Change your wi-fi password make it more secure and they will not be able to print.

You don't need to worry about the printer and pages printed, you need to worry that someone has access to your wi-fi that is a way worse.

[Danni1985]

No that’s not it. They are pensioners, not hackers 😂😂 they printed off some of their bank information this morning by accident. 

They've obviously selected my printer by accident as it isn’t password protected.
When I go to connect to anything, my WiFi comes up, their WiFi comes up, their printer comes up, and now so does my new printer. They all require passwords except for my printer and all I need to know is how to add a password.