Negligence from Vodacom***

I had 36 months contract with vodacom, I asked them to cancel my contract, received a feedback from that it was canceled and it will be closed in December, it turns out that it was not canceled and they handed the account over to MBD and they have been calling me. I explained to them what happened and they also promised to investigate and feedback however none of them did that, the frustrating part is that I got calls from different people and I had to explain everything from scratch. These people are ruining my credit score.