Paying for NO SERVICE

I recently took out an mtn Sim deal, the Sim was delivered and apparently RICA'd. I inserted Sim card the following day in attempt to use it but it was not working, no network, just a dead Sim card. I contacted mtn informing them but nothing was done, about two weeks later I contacted mtn using airtime I had to buy coz I couldn't call them using their not working Sim card and canceled coz clearly no help was being afforded to me. I got reference and later an sms saying it cancelation had been finalized. I am to date getting sms's that I owe them for something that never worked and I canceled too. Went into the branch, taking my time off work to make sure it's canceled completely but still getting harassed to pay for NO SERVICE. Fix this.