I got bitten by this too...
I blamed myself for being careless: I didn’t get around to freezing it before the September cutoff for annual-fee reversals, and now I’m down to -40,000...
I called several departments, and other than a few "sorrys," there were no useful responses.
They also admitted that their policy is not transparent enough and training is not solid, which is why the CS team handling account closure didn’t mention any warning about reclaiming the 100,000.

But no matter who I spoke with, no one could restore this 100,000.

For earlier account-closure DPs, this 100,000 was also not reclaimed. I assume this new policy was updated recently together with the September rule change that annual fee reversals can no longer be claimed at closure, but because of my negligence and not studying it carefully, this happened.

My case clearly shows it was caused by cancel or downgrade, not by what others said about MS or meeting the spend requirement.

So, readers, don’t try this as an experiment. Relationship is the most important thing.

Since it has already happened, we need to find a way to solve it.

Support did not mention anything about a blacklist or a deadline for repayment.
They said I can continue using it, pay it back gradually, or cover it by spending. As for a deadline, they did not tell me. So I understand that if they don’t proactively reach out, I can still use it normally, but the accumulated MR usage part is dead.

As for this closure, the rep said they will not pursue the amount I owe, so my understanding is that this closure will not pursue it either.

I definitely won’t make a stupid decision and spend money just to wipe the points to zero. I’ll still keep a few cards and watch and wait.

The above is my personal datapoint and does not represent the blog’s view. I also can’t call multiple CS reps to verify whether what this rep said is definitely correct. Without data to back it up, if you can’t trust customer service, who else can you trust?

Welcome to all readers to share data so we can solve this together. See you in the discussion area...