I'm not a lawyer, either, but a good friend of mine is. I showed him your post and this thread, and his advice is fairly similar to the above. Basically, reply to the C&D letter with a written letter of your own (make sure you get proof of delivery on the postage; keep a copy for your files; etc.). Your letter should be as polite and as brief as possible, because any extraneous language can and will be used against you. If you write something that can be misinterpreted, it's a safe bet that it will be.
Basically, your letter should: a) acknowledge receipt of their letter, b) state your non-affiliation with and non-operation of the offending service. And that's it. Just the facts. No editorialization. No defensiveness. No snide remarks. No theories about how or why they came to think you were involved, and how they are mistaken, etc. And avoid the temptation to get cute or cheeky. Don't poke the bear.
IF they reply to your reply -- which they very well may not -- then you should lawyer up. If you want to be super cautious, you can consult a lawyer, and probably pay a fair bit of coin in so doing, to draft your initial reply letter.
Basically, your letter should: a) acknowledge receipt of their letter, b) state your non-affiliation with and non-operation of the offending service. And that's it. Just the facts. No editorialization. No defensiveness. No snide remarks. No theories about how or why they came to think you were involved, and how they are mistaken, etc. And avoid the temptation to get cute or cheeky. Don't poke the bear.
IF they reply to your reply -- which they very well may not -- then you should lawyer up. If you want to be super cautious, you can consult a lawyer, and probably pay a fair bit of coin in so doing, to draft your initial reply letter.