Writing to a magazine ombudsman to help you with a current trip is like going on a low-fat diet while you are in cardiac arrest. Not gonna do much to help you right now.

1. Is this trip on one ticket and if so, what carrier's ticket stock was used?
2. That carrier, sounds like it may be JL, ought to be able to tell you who cancelled the ticket or part of it and on what date. If it was PL, there will be an agent code which won't mean anything to you, but will mean something to PL.
3. That information will be useful to you in calling PL as you can point to a specific date, time and employee (by #) and go from there.
4. Only one of you should be speaking with PL and that one person needs to be polite, but firm. Given the amount of money involved, this would be well worth pursuing in small claims court if PL does not make good and you should make it clear that you will. But, do not make idle threats.

As a caution to others, while you should not have to do this, you do. Always, always, always, check every segment of every itinerary with the operating carrier regularly and especially after any encounter in which changes are even remotely discussed. It doesn't matter what you are told by some opaque third-party such as PL, all that matters is what the operating carrier of each segment shows in their records.