Billed for non-existent line

I took out a cellphone contract with Altech in November, as I simply needed a new cellphone. From the time I got the contract, I never put the sim in my phone, as I simply used an existing line that I had. So I was surprised when Altech billed me for voice calls, data and sms to the value of over R3000 in December. After numerous calls, investigations opened, I managed to get them to drop my account limit. They locked the line in December and I have been trying to get them to unlock it for the last two weeks. I have done all the necessary steps: restarted, removed SIM card. I even did a sim swap yesterday for R150. And still NOTHING this morning. ZERO CELL SERVICE. This is atrocious Altech Autopage. You owe money and you need to unlock this line.