A consumer was contacted by a bill collector about a contract they had supposedly entered with a cell phone company. The consumer said that no contract existed, that they were month-to-month, and that they had properly given notice to terminate their account. After extensive discussion with the debt collector the person was told that if they paid $150 and returned the equipment, the case would be closed. They did as instructed. Now they're being contacted directly by the cellular company, that claims additional money is due for the remainder of the contract. How can they enforce the settlement?