The duties and responsibilities of a Billing Specialist include sending invoices and account updates to clients, receiving, sorting, and tracking incoming payments, addressing and resolving client questions and issues relating to invoices, and providing regular, accurate reports of billing data. Billing assistants create and send invoices, keep track of money owed by customers, and update records with new payments and customer information. They also send out reminders for payments and work directly with customers to follow up regarding money owed.