Need help with closed account

I really need help. I’ve been dealing with a closed account for over a year now. I set up internet and phone service and there was an issue with the order and I was told everything would be canceled and I just need to sign up again online. I did that and they never closed the mobile line. Then I called and they said they would issue a credit to close the balance on the mobile line. It was never done. Then I have a balance of almost 100$ that went to a debt collector. THEN I called xfinity again and they said we would credit the remaining balance. Why was I only credited 30$?!?!? then it went to ANOTHER debt collector. I called 3 separate times after that. First time I was told the credit would apply in 24-48 hours. Second time I was told the credit is pending and should take a week for it to apply. THIRD TIME I was told “I’m not sure why they told you that, credits apply instantly. Also I don’t see ANY notations on the account you’re calling about. Last notation was may of last year.” Then they said they’ll credit my account AGAIN and still nothing. I have zero clue what else I’m supposed to do. Someone from Xfinity please help me.