If you can't wake them up try leaving some poor/mediocre stars. If they are 4.1 now it should be enough to prevent them from listing.
If they file a NPB on you make sure to clearly comment in the dispute the reasons "seller increased shipping charge after listing ended". This way you can easily appeal any strike you might be given and also retain the right to leave feedback.

"What else could I do? I had no trade so I became a peddler" - Lazarus Greenberg 1915
- answering Trolls is voluntary, my policy is not to participate.