FAILURE TO DO SIM SWAP

I lost my contract SIM Card in January 2020 and I went to the branch at President Hyper in Johannesburg and I paid R150.00 for the SIM swap and was advised that the SIM will be active within 24 hours. SIM is still not active. I visited the branch plenty of times with no success, I call the branch everyday and they are not answering my calls when I call them now. When my SIM got lost there was airtime in it and on the 12 of every month I receive airtime and now I do not know what will happen to this airtime that I am paying for every month. I have never missed a payment but now I feel like I am paying for nothing. I WANT TO CANCEL THIS STUPID CONTRACT