Reprocessed jelly still not setting up

I have a blackberry watermelon jelly that I made and it didn't set up. I waited about 3 weeks for it to set up and then reprocessed it, adding more pectin. I added 1 1/2 packages of pectin (it was a large batch) and it still didn't set up. I've looked on-line but can't find anyone who's actually reprocessed a second time. People have asked but no one has done it to answer. Can I reprocess it or do I just have to resign myself to having syrup? lol