Passcode change issues

I want to change my passcode and I keep getting a message that the code is too easily guessed. It is MY phone—not given to me by my employer nor do I use it for anything related to work. I’ve tried several six digit codes as well as an alphanumeric code. Nothing works. I get the easily guessed message every time. Also, under passcode options my only option is alphanumeric. I don’t have a choice for four digits.

The phone made me change it a few weeks ago. I don’t like the code I picked then and would really like to change it.

Thanks