Why not just tell Fidelity to do a rollover from the "IRA" back to the plan. Fidelity will issue a 1099-R for this, and the plan does not file a 5498, so this will eventually result in an IRS letter. I got one myself when I rolled from my IRA to my plan a few years ago. But a simple response that it was a rollover from the IRA to a qualified plan took care of it.
Yes, it is not really a rollover, as it was never really a distribution. But it fixes the error and it is explainable, especially if the documentation for the original IDA request is clear that no distribution was ever requested.
Life's too short to fight Fidelity.