This is an old post (and I notice the only commented shares my love of Chavin!), but I will answer anyways...
Best thing to do with San Pedro in a situation like that is to ask him what to do. San Pedro is pure light - no darkness, so he will always give you good advice in my experience. San Pedro also offers you powerful protection just by drinking it, so you are starting from a good foundation!
I find when you ask San Pedro to guide you through experiences like this that the process just unfolds naturally from there - you just gotta open the door.
I can share one story... Not of a demon, but when someone sent a magical attack to me.
Normally I have the best luck... But suddenly I had this weird string of bad luck - one thing after the other, and the weirdest things that should never in a million years all happen at once. Everything that should have easily worked out instead was going crazy and wreaking havok - it was really weird and confusing.
So I drank San Pedro and asked for clarity on this and a solution. He showed me that someone online who practices Enochian magic had sent me a attack because they were mad at me. I did know the person, and while I thought they were more mature then that, in some ways I wasnt super surprised... But San Pedro didnt have me send back the energy or retaliate - San Pedro taught me something else.
When someone sends you bad energy, you can easily change the form of that energy. All energy changes forms, and once the send it to you they have let go of it and it is now your energy, so you can do whatever you want with it as long as your recognize it and work with it. You can turn harmful energy into something empowering.
So I made a dispatcho offering to mother earth, sang a song, and smoked a lot of mapacho. My luck shifted right then and the crazy string of bad luck turned back into my good luck, and the bad things that had been happening turned into opportunities that were really awesome! It was a tough 2 weeks before that offering happened, but so good after the offering.... The guy had sent a lot of energy my way, so once I "digested" that energy and turned it into nutrition for my life it was really a big boost - and in some ways it probably created some good energy for the dude who sent the attack (apparently he needs some good energy!).
So, that wasnt stuff someone taught me to do, or that I knew to do in that situation.... That is all just what happened when I asked San Pedro what to do. Asking opens the door