I need to contact executive customer support

I been with Xfinity for about 9 years now , everything was ok until I was offered free mobile line in end of May while i'm returning internet device for one of my houses because I was going to stop the service , the rep. told me that i'm eligible for free line , I told him i'm returning a device to cut off service , are you sure I'm still eligible for that offer , he said absolutely , I said i'm travelling overseas in few days , do you think I can activate the service when i'm back , he said yes 

long story short , the sim was delivered while i'm away from home , and I start getting billed for non active mobile line without activating the line , when I came back got with customer support to fix this issue and make sure don't receive future bills and line is not active , they said you will get a credit for those 2 bills and your line is no more active , received credit , but Xfinity charged me another 2 bills , when I got with customer support few days ago about that issue they said we can't do anything and also said your line was still active , also said I have to return my own device 

please I need someone to fix this issue for me and also need refund for the bills I was charged for 

thanks