I would be kind of tempted at this point after getting a partial credit to chalk it up to something odd and move on, provided it doesn't happen again. If it ever happens again though, I would be asking for answers.
I hear you.. I do think that is probably where I am heading with it. I'll wait and see what they come back with. Verizon told Apple and I to not expect any flexibility if it happens again and Apple has given me instructions on what to do if it happens again, although it seems to be a one off incident.
It just leaves a bad taste in my mouth. Verizon has gone above and beyond here (eventually) as they probably didn't have to do anything. Apple on the other hand needs to figure it out. It shouldn't just be - "here's a bill, pay it and don't ask questions even though we can't explain it."