Horrible customer service and billing

i canceled my xfinity mobile line last year and had to call 4 more times this year with promises i would get a credit back for the canceled line and now i have a $357 bill and collection notice. my last bill shows a $233 additional charge that doesn't even show what it is for? the billing and customer service is horrendous. it shouldnt take me fighting to cancel a line for 10 months. I'm supposed to get a refund, not more charges, what is going on???? I couldn't even get service at my home and you have record i never used the phone line but still kept charging me monthly and promising it would be canceled and I'd get a refund. this is ridiculous