Everything in my notes app suddenly disappeared. iCloud notes were recovered but the notes on my iPhone account, that have been there since 2009, are deleted. All of my important info was in those notes. Please help!!

One morning, everything in my notes app was gone. I didn’t make any updates or changes to my phone. This occured spontaneously. I called Apple and they informed me that it must be a glitch with my notes app and that they don’t think all the information was gone. He told me to update my iPhone. Once I updated my iPhone, only the notes on my iCloud were there. All of the notes that were on my device are completely gone. I have been storing data in my notes app since 2009. I rely on that app for very important information (passwords, account info, account numbers, reminders, letters, date keeping, etc.). This is unfair to me a loyal customer. I could understand if this occurred as a result of a back up or something that I did on my behalf but that is not the case. My notes of all things is supposed to be safe on my phone. There has to be some way for me to get that data back. Please help.