********** airtime taken from my account

I have an old account with Edgars and in 2015 an airtime of R1000 was taken out of my account. I was shocked when I noticed that and went to Edgars many times to complain and the employees did not help me. When I asked for a manager they said the manager is not available. I told them that I had a company's free contract phone how can I take such a lot of airtime. I continued to pay by debit order and when I went to check it yesterday they say I'm the one who app**** for that airtime. Please help.