eBay Buyer Fraud/Scam - what can I do?!?!?!?

[Billyscards]

I've been selling on eBay for 10+ years and this past week had something that has never happened before but is causing me to challenge my thought process on moving forward with selling on the platform.

If anyone has advice on what I did wrong or what I should do I would greatly appreciate it.

On March 23 - buyer submits a best offer, I countered and the buyer accepted the counter and paid for the item immediately. Address was US based and everything looked fine.

March 24th - I mail the item with tracking/etc.

March 25th - I get an email from eBay "Suspicious buyer for item" - and they were cancelling bids and removing the listing because they aren't registered on eBay. Says to not ship however this was obviously already done.

April 4th - "Buyer" opens up a dispute that the card wasn't received. Even though on the tracking it shows that the item was delivered on March 29th.

April 6th - can't get a hold of eBay.. paypal says its an eBay issue. I have to respond to the buyer and then wait and then "ask eBay to step in". I'm thinking since the listing was removed. Paypal is holding my funds and I have a feeling I'm going to come out on the wrong side here.....