> It's reasonable that the providers expect to have a way to enforce the contract.

No, no it is not. Contracts are legally binding and therefore enforcement should be done via legal means. This type of behavior is nothing short of vigilantism.

Beyond that, this type of behavior is anti-competitive. Carriers should compete on service and customer satisfaction, not how much of a margin they can eat to entice customers into contracts. This type of scheme naturally favors larger companies and acts as a way for industry incumbents to retain market market share.