hp printer wont let me register it

[User_8489092]

Maybe someone can help me here, this is driving me crazy.

I bought a new laser jet printer with scanning function and double page printing yesterday. I bought it as one of those "has been opened but as good as new" from the store.

I downloaded the app, set up the printer no problem, until it comes to the part "register my printer". Neither on my android phone or tablet will it let me register it with the pin number. It says the pin number is not correct (or something similar). 

I have restarted both printer, apps etc. from scratch.

And of course to get help with my product to get it registered it needs to be registered to contact customer service...

What I am wondering if the people before me registered it, printed out a bunch (cartridge is approximately 40% full) and then delivered it back. 

How do I go from here to get it to work? Please help, thank you.

EDIT: I also tried to follow some general instructions by going on advanced settings to do a factory reset. There I also had to put in pin number, which was not registering either.... Also it works fine with the wifi and connects easily to the apps, but I can't use it since it's not registering with the pin number

EDIT EDIT: Getting support from HP is completely impossible, and the only thing they recommended was go to the forum, unless I register my product.. there is no phone number, chat or email I can contact HP and get proper help from. If I don't receive any help on how to solve this I will return my printer tomorrow (monday) since I *need* a printer now to print documents and can't afford to wait to see if anyone comes back to me. It seems like a really nice printer, but this is hopeless....

[Valsimot]

And the printer model you are referring is ?

[User_8489092]

HP laserjet MFP M234dw