BILL CHARGE UNEXPLAINED

I left SA on 30 January 2016, in February 2016 I was billed by Telkom for the amount of R405.50 Reference TELK***C. I don't have a Telkom account and settled everything with them before I immigrated to the UK. My Telkom email was [Email Removed] and the landline ***. I didn't have any outstanding money owed to Telkom and want to know why they have unauthorised debit out of my bank account! I sent my son with a certified copy of my ID to go ask on my behalf as I now live in the UK and they were unhelpful. Who has taken my money. I want it back in my bank account!!! I have sent them 3x complaints via their website and no-one answers me.