Is it possible the person is using airplane mode, in a location with limited connectivity, or maybe blocking you?
When you say you have "tried everything" it's usually more helpful to list what you have tried or include a link to troubleshooting steps that you have gone through.
No they are not on airplane mode because they have school and we recently talked via call, I've tried turning on and off my iMessage, reset my network settings (that's everything I could think of) I just tried turning off my iMessage again and now the person I'm trying to text won't go back to iMessage even though they have a iPhone and it's worked previously
Are you able to send an SMS to them? Do they have iMessage turned off?
i message not sending to one person