Deducting money from your account without proof

I have a contract with Autopage for 18 years. Recently Autopage deducted a large sum of money (+R2500) from my account, apparently for data. History for the years prior indicates no high data usage trend. When I requested proof of the data usage, autopage could or would not produce this proof. I have now tried 4 times to resolve this issue, of which twice I went into their head office. I have received numerous promises that the issue will be resolved, but no joy. I have not used this data and they simply sent a mail to say I did and offered no proof.