It certainly feels illegal to have the threat of a ban when you make a good faith report of fraudulent charges. A business could have a pattern of deliberate overcharges that they layer in with regular transactions with the knowledge that enough users will just give in and eat the fraudulent charge to avoid losing access to the service. If the business has run the numbers and found that it's a net gain in profits from this practice, there would be a reasonable (if completely corrupt) motive for operating the scam.