Money owed to client

Been a loyal customer to them for 10 years. I recently cancelled my services as they do not cover my new place I moved into. I ordered a new line with the router for 250 rand. And I paid it using EFT. Then they also debit ordered another 250. When I canceled all the lines they made me pay the cancelation fee but could not give my 500 rand back or even used it as deduction of credit on the cancelation fee. For some reason they also struggle when it comes to paying cliets back.