Domain Industry in Asia   SUBMIT

Hi all, ​ I own an internet domain name. For the sake of remaining anonymous, let's refer to it as []( I've owned []( since 1997 when I was the original registrant, and I use it to run a small website which earns me about 60% of my current income and basically pays my rent. ​ I received a certified letter from the legal department of a Fortune 500 company. Apparently they own the trademark ABCD and are demanding that I transfer ownership of the domain name to them or they will take legal action. They also state in the letter that since I am "willfully" violating their trademark (my website makes no mention of them and is actually a completely different subject matter) that they will not entertain purchasing it, they are demanding I just hand it over. However I used the USPTO trademark search and discovered their trademark wasn't registered until 2018 (and is based on tech they developed in 2017). My use of ABCD pre-dates theirs by 20 years. Over the years I have done internet searches on ABCD (to see how I ranked in search listings) and until last year I was always the only result, so I'm pretty sure I was the first to establish the phrase ABCD. ​ I flat-out can't afford an attorney to fight this (even scraping together money to buy groceries beyond March is going to be an issue). I have not answered their letter yet. It feels very much like they are trying to bully me legally. But losing this website and its income would be a near financial death-blow to me. I'd lose my apartment and my car for sure. Is there anything I can do to defend myself? ​ Thanks in advance. ​ Edit: I'm in California. Sorry for omitting that, I'm rather flustered about this whole situation.