Cancelled contract and still being invoiced

I cancelled my contract with Telkom Mobile (having expired a few months before) the 1st of November, 2015. The final debit order was confirmed to go off as expected the 30th of November 2015, which it did. I also ensured that the spend limit of my account was R0, so i could not spend more on call/sms/data costs over that which i have received bundled with my plan (which i did in October already). The debit order seemed to have stopped, however I have received an invoice for the usual amount dated January 1st, 2016?