Billing on already closed account

Hi, I am talking to verizon for over a month now and it looks like there is no resolution for the issue i am facing even after multiple reassurances. 

I ordered home internet 5G device of 10/09/2022 received and activated it 10/12/2022

Returned this device on 10/24/2022. Account was disconnected.

10/27 - Disconnected account still sho wing $80 due, called Verizon. They said $80 credit will be applied in next bill

11/13 - next bill still showing $80 and its past due now. Called verizon was asked to wait for next bill.

12/13 - now this is $334. With one time charges and all. Is there a way i can get my billing issues actually reolved? From not owning anything to $80 and now $334. I don’t know what to do.