Mercari complaint: Refund Refused

I purchased two mugs on Mercari as a gift for a friend. The seller had neglected to properly pack the boxed mugs with bubble wrap or another shipping material. One of the mugs broke in transit. On Mercari’s website, they instruct buyers to try and resolve any problems with the seller first.
I contacted the seller and she admitted it was totally her fault. She said she would contact Mercari support to request a refund. After a few days, I contacted the seller again to ask about the refund progress. She stated that her Mercari support contact person, Chris, said she would look into the matter. The seller said she would contact them again. After unsuccessfully searching on Mercari’s website for a contact email or phone number, I gave up and searched online for the information. I reached out to Mercari and was told that even though I contacted the seller first as directed by them, I should’ve also notified them. My direct inquiry fell outside their 72 hour time frame for a refund, so I was ineligible to file a claim. The seller got paid for improperly packaged items and I paid for her mistake. As a consolation, Mercari Support offered a 10% discount on a future purchase of an item costing $20 or more. In my opinion, that was not an offer, but rather, an insult. I have filed a disputed charge claim to my credit card company and will be closing my account on Mercari as soon as my last purchase is delivered. I want to rate my seller so she can get paid in a timely manner.