When you sign up for any trial, it is always a good idea to set a reminder (with the date it ends) otherwise you basically agree to continue your membership at the end of the trial if you don't cancel it. If you never signed up or never clicked on any link starting your trial, even by mistake, you have to contact eBay via live chat and explain your situation. I never signed up for the eBay Plus trial, so i don't know, but I assume they might send you an email when the trial starts? Maybe you can check your mailbox.
