DMC
Unauthorised debit orde

I have tried emailing company direct, but recieved no response.
I received a call Last wednesday (13/8/2013) from a lady claiming to be from DMC. Asked her to call back in an hour to discuss whatever it was she wanted as I was busy at the time. To date I have not recieved any call back, nor have I changed my contact details.
This Tuesday (20/8/2013) a get an SMS notification that DMC has submitted a debit order. Now:

1. where did they get my bank details
2. Who authorised the debit order
3. What is the debit order for?

Company: DMC
Country: South Africa

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