This “charge you forever for a product with a one-off cost” method is what phone companies do too in “selling” you a handset. Which is why you should get a SIM-only contract and buy the handset yourself outright. (Even credit card interest is lower than phone contracts.)https://twitter.com/zeynep/status/1022852170926964736 …
Arguably there should be a legal prohibition against selling both a product/service and selling credit, which is what they're doing, since the two get muddled together in ways that are always deceptive and damaging to the customer.