Account Past Due, Called multiple times trying to get account up to date with no result

Hello I am messaging as a last resort as I have tried contacting Xfinity customer service, collections department, and the online messaging system. I got an xfinity mobile account with an iPad a few montha ago as a bundle deal to help lower my internet cost. I signed up and had autopay set. I was not made aware that there would be two seperate bills. I now seem to have a disconnected xfinity mobile account with a 500 dollar balance. I have tried everything to get my account back up to date and put the ipad back on installments. Nobody has been able to help me. I have been a loyal xfinity customer for years and did not know I had a seperate bill.