Prepaid and postpaid accounts

Hi, my name is Maria and I have been customer of T-Mobile for many years. I have a prepaid account with them, recently I decided to give them a chance by getting home internet. Now because I already have a prepaid account with them I can't get another account to manage my home internet account unless I change my email on my prepaid account which I did four days ago but I still can't get a T-Mobile account ID to manage my home internet account. I have been on the phone with customer support multiple times without any success. please