They review (and usually increase) prices once a year, in much the same way that many other ISP’s and indeed other companies in other industries do. The obvious exception being where you go from a discounted contract rate to a rolling 30 day account (though it sounds like you don’t stay that long), but that’s not an actual price rise as the service price remains the same, it’s the end of an introductory discount, which can easily be re-applied with a phone call, a little honesty and a new contract, same is true most of the tine with annual price rises. Personally that seems like a much simpler and easier process than multiple credit checks and having to be available for multiple installs, but some people enjoy finding overly complicated way to do simple things.