Incorrect debiting of account for three months

A cell phone contact upgrade was approved accidentally. The cell phone was never delivered by the supplier and it was requested that the contact upgrade be cancelled. The Supplier debited my account despite requesting the cancellation. After consulting with the supplier they credited the account for the months billing and confirmed the upgrade has been cancelled. The product was in the suppliers possession and had never been delivered. My account was subsequently debited for three months despite never having received the upgrade and with confirmation that the upgrade of the contract had been cancelled