Double billing

ADTcsecurity in Witbank installed beams at my house,I was told to make a cash deposit and I did that.A month later I was billed for the same services and my account was debited.I notified them about this and the accounts department in Wurbank confirmed that they received the payment .Now their headoffice in JHB won't pay me back because they claim that they can't find the payment even though I have sent them my POP on numerous occasions.