Try pulling just the border off without soaking it or using a stripper. Sometimes you can get the top part off and expose the backing under it and then you can just remove that by getting it wet. There is a good chance though that when you pull on the border, you will be pulling off the wallpaper too....that's just how it goes.

You need to seal the cardboard area, apply joint compound and then sand it smooth. prime and then paint.

Sorry to hear about your experience. Mine is/was similar. I found several layers of wallpaper, with a skim coat in between, and then under that, it seems to have been applied directly to drywall. I have removed a lot of wallpaper in the past, but I ended up damaging the drywall in one room so badly, we decided to hire someone. I had several contractors come through who looked at the amount of wallpaper and wouldn't do it! One guy was willing and he starts this morning so I will see what magic he uses. If he has any tips, I will share.

Thanks for all the suggestions!! I wish I would have realized it was glued directly to the drywall before finishing the whole wall 🤦🏻‍♀️ live and learn for sure! Definitely going to seal the problem wall, skim coat, then texture and prime/paint. Then just skim coat over seams of existing wallpapers then oil prime over it. Question though! After applying the texture do I need to reapply the oil based primer or can I just use oil based paint/primer? There sure are a lot of steps and lessons learned here. In our bathroom it just pulled right off, it was prepped correctly. This room was an add on room so someone differently did it.