I'm pretty sure that anything sent through email can't be taken legally. And even if the post to your address a letter they have to ascertain that you have read and acknowledged the letter (conceivably your pet dog/girlfriend ate all such letters placed through your letterbox).
The first thing they have to do is get you to write back saying you acknowledge their concerns and admit to selling a pair of jeans. They then have to prove you are either a business or a black market dealer selling counterfeit products.
Since you have sold a single product and are not a business then this is not a problem. They would have also needed to receive one of the counterfeit products you allegedly sold. Furthermore, they would have to rpove that you were willingly buying and selling counterfeit goods. Finally, above all, they have to prove that this isn't simply someone selling some unwanted items- which it is.
IGNORE