MEO does that in Portugal. With your phone you visit (probably) an ad on a website and you're automatically subscribed to some 3rd party service that charges 3€ a week from your mobile operator credit.

Then you call MEO to cancel the service and then you learn they're not refunding your money and that instead of this 1€ call you could have disabled the 3rd party services through their web login.

It's incredibly hostile, and there are more dirty tricks they use.