Shocking service

I received an data usage bill in August 2015 which until now has not been rectified or settled. they have now sent me a final demand letter but cannot prove what the data was used for as the sim card has been locked in my office drawer.<br> We have a corporate account with Vodacom without any issues but my personal data contract is a mess. <br> I have sent numerous mails to the call centre without any positive results and they keep submitting the amount for payment but i refuse until they have proof.