Double debit

My account has been double debited since May. I've phoned Vodacom more than once and gone instore to query the double debit and there is no record of it on the system. I've returned the last two debit orders and put a stop on it. Vodacom has now sent me a second letter regarding the 'outstanding' amount. Even if I go online to pay the so-called outstanding amount, there is no record of it on my online profile. Vodacom actually owe me money for the double debits.

This is not the first time I've had issues with Vodacom billing me for services I did not receive or sign up for. Last time it took 6 months to sort out.