Nope, they dont even need a CC number. They do occasionally send renewal letters but just disregard them.
I've been getting free magazines for years and have been giving subscriptions to my family all the time. Magazine companies only get a fraction of earnings in the subscription fee. The most money they make comes from advertising.
More reader base = increased advertising fees
They dont care about your subscription fee, they do care about statistics when they present to advertisers.
Ps, I had a magazine subscription (I think it was PCmag) that runs until 2017.
ding ding we gots a winner!!