IMEI reset & crucial data backup

[AC Question]

Hello
My Elephone P9000 lost both IMEI Numbers while I was flashing it from Android 6 to 7. Unfortunately IMEI changing apps won't work and the option to change them in the EngineerMode won't show up either.
I've been trying to find a solution for several hours now and I'm completely out of ideas on how to get the Numbers back, they're on the package so I know which numbers I need at least.
Another questuion I have is how I can backup data like this.
Before I figured that I've lost both IMEI's, I didn't knew they existed so I couldn't make a backup of this data. So before I try rooting and such that could potentially harm more data, I'd like to backup all the stuff thats deeply ankered into the system, I don't really care about apps, conacts and picture files at this point.

I've tried out a tutorial on techrepublic regarding that already, with no success since the backup file contained no data at all.

I really hope to get some help here, thank you for answers.

 

[Rukbat]

To back up, see Backing up an Android Device. As for the IMEI (there should be only 1 - if there's a hex number and a dec number, you want the dec number. (They're the same number, one in base-10 arithmetic, one in base-16 arithmetic.) http://forum.xda-developers.com/attachment.php?attachmentid=2654643&d=1395976263 and https://forums.androidcentral.com/e...m.themonsterit.EngineerStarter&token=E6HmP-qx are supposed to allow you to enter the IMEI number (use the dec number).