How frustrating! I've been pumping for over 25 years, and it's been my experience that once you "pull a cannula out", it's out. This may not be the case for metal cannulas, but I'm assuming you're using teflon.
all pump companies are going to have 24/7 support lines. give them a call! I had a bad box of sets once, it was in my first few months pumping. I practically ended up in DKA. maybe next time you change out, try a different box.
let us know what happens.