CellC contract offer

I was offered a cell c laptop contract, i was promised it will be delivered after 7 days, i have not recieved a call nor delivery of the item from sell direct. My worry is that i gave them my bank details and they might deduct money from my account without the item being delivered (based on the reports that i have read about the company). I want to cancel the deal because they have not met their side of the deal, been trying to call them ***/ *** no answer. I have emailed Marco he is not responding.