one year free line - but i am getting bill every month

i switched carrier to xfinity as new customer and they offered one year free line. next billing cycle onwards i am started getting bill for two line, which i activated only one. connected with customer care support. seems they wrongly removed my free line and now i am getting every month bill. i raised complaint to change this line as a free. still now i have not got solution for this issue. every month i need to call customer care to get a credit for my billing. is that the way to give solution for customer.