Hi I can't find the key, which is in the belly...of what?

The way yu get the key is by going to the bathroom where Melanie was at and yu will get a chainsaw them go to the iron door where it says the key is n the belly and touch the door then it'll try to cut it with the chainsaw but it says that the chain has bounced off then after that go to the guy that had the pig mask and touch him n yu will pick him up and put him on the table and then get out the chainsaw and cut him open but yu wil go to a bad end

Unfortunately, it's impossible. You need to get the meat out of the oven first.

The code to the oven works, but you'll need to twist your phone around. Some people said it worked flipping their phone, and mine worked when the right button was South (S in SEE NEWS).
You'll find some meat and when you cook it, it'll have roman numerals to allow you to go back to chapter one and use those numerals on the closet instead of the code on your knife. You'll find the can and briefcase, and after you chuck the briefcase out the window, you can spray the window and allow yourself to slam the window on the pig-man. This will result in you KEEPING the rope. That is used to tie the pig-man (whether you spray or stab the first time doesn't matter). NOT killing him and trying to leave will trigger the True Ending.

Go to the bathroom then you will have a chainsaw, touch the iron door after that go to that stupid pig pick him up and use the chainsaw