eBay Vendors

Do I sign this paper from the lawyer?
I sold something on ebay and it got knocked off due to Trademark Infrigement. In my title I said the competitions Brand Name. When ebay let me know what I did wrong I change my title and wording to make sure I was not doing anything wrong…So after about a week of not having the BAD item for sell I get a letter overnight express from a Law firm from the company, I already stopped doing the trademark infringment once I knew what I was doing wrong…they emailed me once and i told them No Problem, I wouldnt do it again,..anyways I got a letter from the Companys law firm about how I broke the law and …This is the last few paragraphs…they want me to sign it and I am uneasy to sign it. I cannot afford a lawyer.
"In view of the importance of this matter, we hereby demand that you return a signed copy of this letter Feburary 10th, as a written assurance that you agree to the terms of this letter. If we do not recieve a satisfactory response from you by then, The ************* Company reserves the right to take any action it deems necessary protects its valuable intellectual property right. This letter is sent without waiving any of the ***** Company’s rights or remedies, all of which are expressly reserved.
That is the last bit of the stern letter, If I sign this will it all be over, or if I sign it, am I digging myself into a hole? Any advice would be great, I cannot afford to hire a lawyer. I know I was wrong, And I told the company once in a email, I would not do it again, and now I get this letter. Also…How did this company get my Home Address, I didnt know eBay gave out this kind of information, unles this company bought one of the items from me to get my address..
Thanks for your time, I just dont know to sign or not.
This was not a counterfeit item that I was selling, The Brand is the real deal and is not copying any one, but I identifiy another brand while explaining my brand. That was my bad. I know it was wrong, and I admitted that, I dont need no one telling me that, just do I sign or not? I dont want to get myself in any more trouble. thanks agian

If it wasn’t served to you, or sent certified mail, throw it away and act like you never got it.

Added:
The reason I say this is that anyone could have saw your original eBay auction and sent you this letter. You don’t know that it’s a law firm because it has letterhead.

Google the law firm’s name and see if they are legit. Do the same search using the word fraud. See if the phone number on the letter matches the business number from the internet. Then call them and see what’s going on.

If it is legit then I would sign it. Do your homework first though. That won’t cost you anything.
References :

yes sign it you are just signing it to show you will not do this again. that is all. It will take you out of this mess and be careful on the web when you are doing something.
References :

Tell them that the issue was resolved…That they are harrassing you…and if it doesn’t stop…You go to the press…Take care
References :

DO NOT SIGN IT!

It almost sounds like it could be a scam! You have to get some other advice but if I were you I would not sign it! It willdigg you into a deeper whole if you really did not do anything wrong and you fixed the problem then it should be a problem!
But you can hire help and sometimes they have help for free for less fortunate people who can not afford it.
I hope this helps.
References :

You were selling a counterfeit. You got caught. This type of letter is normal. Sign it and don’t sell counterfeits - regardless of what you call them. Or don’t and take your chances that the company will not sue you.
References :
20+ years practicing law