I cannot access my magazine subscriptions in itunes

I am so frustrated with this issue. I purchased magazine subscriptions on my ipad that are automatically renewing and I cannot access my account settings in itunes or wherever i need to do that. When the email comes to me about an automatic renewal, I click on account settings in the email and it takes me to a link with an old email address. When I put in my correct Appple ID email address (that the email came to!) and password, it continues to say it is not correct. So then I changed my password and the same thing keeps happening. I am just confused. Is the magazine subscription through itunes? Isn't my aple ID for all things apple?