MTN praying on pensioners

My mom who is a pensioner and has always had a MTN contract, was sold another contract by some ******** from Mondo. When I realized that I immediately canceled the contract and arranged collection of the equipment within 14 days. I spoke to them and was assured that contract was canceled. This was in May, sadly MTN has been billing my mom for this contract which she can not afford and was not supposed to be sold as she could not afford as a pensioner. This has resulted in her existing number to be locked. We have tried calling call center to get to no avail. This is so heart breaking as she now has to rearrange her because MTN will not help her. I'm a Vodacom employee and I really regret allowing her to remain with MTN as this is so easy fix with Vodacom.