You never should have been using it, though? It wasn't your domain to begin with or your TLD. It's like complaining that you're using appname.ycombinatordev.co

You never should have been using it, though? It wasn't your domain to begin with or your TLD. It's like complaining that you're using appname.ycombinatordev.com as a development suffix, then someone registers it and all your stuff breaks, and you want them to fix your problem. It isn't good practice to use random domains or TLDs that you don't own for testing. At work we have a separate publicly-registered domain, and an internal subdomain with NS records on the primary publicly-registered domain that resolves separately. It's never been a problem..