Don't use the form. Use the legal way to quit any contract in your country. For instance that means sending a paper letter to their offices with the postal service confirming that the letter was received. If your contract has a quitting period pay the 3 months or what. Then stop and ignore all the annoying emails and letters they send you. They will not sue, because they would lose.

Might cost you $5 for the special letter type, and might cost you 3 more monthly fees than you would be willing to pay otherwise. But this is 100% save in all countries with a working legal system. Of course if they come after you with baseball bats or car bombs, then you probably can't quit their "services" anyways. ;)