Neither a doctor nor his medical practice were “debt collectors” within the meaning of the Rosenthal FDCPA, as the doctor and medical practice did not regularly engage in the business of debt collection but instead hire third party billing services to bill and collect for their medical services. To be regularly engaged in the business of debt collection, a person must personally engage in debt collection, not just hire others to perform that function. Cavalry SPV I, LLC v. Watkins (2019) 36 Cal.App.5th 1070 is distinguished as involving two affiliated entities, one of which collected the other’s debts. Here, the billing service was unaffiliated with the doctor and his medical practice. The doctor and medical practice were also not liable for the billing service’s violations of the Rosenthal Act. Normally, debt collectors are treated as independent contractors, not agents, of the parties for whom they collect debts. Here, there was no evidence that the doctor and medical practice controlled the manner and means by which the billing service collected debts.