Moving out but roommate is staying in current apartment

I am going to move out of my apartment soon on my own but my roommate is going to be staying in the apartment. We currently are renting an xfinity modem and we want to keep the modem for my roommate to use. I am the one who created the account for the apartment and I was able to make my roommate the manager of the account but xfinity is not letting me create a new account so I can start wifi at my new apartment (the website says my phone number is already associated with another account). I had my roommate remove me as a user from the current apartment's account but then I can't log into my xfinity account after being removed. I tried to reset my password to log in and it just brings me back to the old apartment account instead of letting me create a new account. I tried selecting the moving page but it asks me to list a date to cancel service to the current address. Even though I made my roommate the manager of the account and she changed everything to her name and phone number, my own phone number is still associated with that account. 

I want to be able to leave the current account so I can create a new one (I have my own modem) and have my roommate be the sole owner of it so she can keep the rented modem (for ease of transition).