Prepaid to postpaid ERROR

On the 3rd of this month I signed a contract for a Motorola Moto g5s plus on freeme 500mb topup. Instead of being issued with a new number I opted to use my existing prepaid instead which is ********** . I didn't insert the simcard on the phone while in store since I had forgotten it at home. When I arrived I inserted it, and the simcard was dead already. I then called telkom on 180 and the call center agent explained that my simcard is undergoing convertion from prepaid to postpaid which might take up to 24 hours. I waited 24 hours and my simcard was still dead and when I call 180 they tell me that my number is active and on a phone, I then decided to go to a telkom direct store at Hatfield and asked for a sim swap. After a sim swap I was able to regain my number back, only to a shock that someone was using my number and they had used up all my monthly data and we're even making calls. And on the 6th I was receiving calls from a man by number ********** claiming that my number is his wife's recent new sim number that she had recently got. I tried explaining this to both staff at telkom direct store and call centre and all they can say is that there is nothing they can do I just have to foot the bill. I then asked to cancel the contract under 5 days cooling off period rule, they then said I will still be liable for R800 cancellation fee and remaining months. This experience has totally changed my perception towards Telkom. I had high hopes in Telkom thinking that it was doing things differently from other network providers. I am now going through the whole month without data and Telkom is refusing to take responsibility at all means to such a point that one lady suggested that my consumed all my data the moment I switched on my phone.