Take them to small claims…
Take them to small claims court. Depending on your state, the limit for small claims court will be around $10k-$12k. It's not hard to do and the cost to file a claim is small. Believe me, that will get their attention. Make sure you have relevant service documentation. This is a last resort, but there's a good chance you will prevail if you're honest and prepared. It's surprising this wasn't mentioned in the article.