Same thing is happening to me

I have Xfinity internet and mobile.. we pay every month on time for 2 years now. I already got a letter say sing I owe them 305.17 yet I contacted CCS to tell them this is [Edited: "Language"] and I have no idea [Edited: "Language"] this is.. they said okay and acted like it wasn’t a problem never heard about it again.. now 3 months later I get another letter saying the same thing. Like [Edited: "Language"] going on???? How do I owe you anything ? And if I did why wouldn’t it be on ANY BILL OR APP? Just All the sudden a collection letter?? 
y’all need money that bad to make up people owe you ??